Rework diff rendering to allow putting the cursor into deleted text, soft-wrapping and scrolling deleted text correctly (#22994)

Closes #12553

* [x] Fix `diff_hunk_before`
* [x] Fix failure to show deleted text when expanding hunk w/ cursor on
second line of the hunk
* [x] Failure to expand diff hunk below the cursor.
* [x] Delete the whole file, and expand the diff. Backspace over the
deleted hunk, panic!
* [x] Go-to-line now counts the diff hunks, but it should not
* [x] backspace at the beginning of a deleted hunk deletes too much text
* [x] Indent guides are rendered incorrectly 
* [ ] Fix randomized multi buffer tests

Maybe:
* [ ] Buffer search should include deleted text (in vim mode it turns
out I use `/x` all the time to jump to the next x I can see).
* [ ] vim: should refuse to switch into insert mode if selection is
fully within a diff.
* [ ] vim `o` command when cursor is on last line of deleted hunk.
* [ ] vim `shift-o` on first line of deleted hunk moves cursor but
doesn't insert line
* [x] `enter` at end of diff hunk inserts a new line but doesn't move
cursor
* [x] (`shift-enter` at start of diff hunk does nothing)
* [ ] Inserting a line just before an expanded hunk collapses it

Release Notes:


- Improved diff rendering, allowing you to navigate with your cursor
inside of deleted text in diff hunks.

---------

Co-authored-by: Conrad <conrad@zed.dev>
Co-authored-by: Cole <cole@zed.dev>
Co-authored-by: Mikayla <mikayla@zed.dev>
Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>
Co-authored-by: Michael <michael@zed.dev>
Co-authored-by: Agus <agus@zed.dev>
Co-authored-by: João <joao@zed.dev>

crates/multi_buffer/src/position.rs

@@ -0,0 +1,264 @@
+use std::{
+    fmt::{Debug, Display},
+    marker::PhantomData,
+    ops::{Add, AddAssign, Sub, SubAssign},
+};
+use text::Point;
+
+#[repr(transparent)]
+pub struct TypedOffset<T> {
+    pub value: usize,
+    _marker: PhantomData<T>,
+}
+
+#[repr(transparent)]
+pub struct TypedPoint<T> {
+    pub value: Point,
+    _marker: PhantomData<T>,
+}
+
+#[repr(transparent)]
+pub struct TypedRow<T> {
+    pub value: u32,
+    _marker: PhantomData<T>,
+}
+
+impl<T> TypedOffset<T> {
+    pub fn new(offset: usize) -> Self {
+        Self {
+            value: offset,
+            _marker: PhantomData,
+        }
+    }
+
+    pub fn saturating_sub(self, n: TypedOffset<T>) -> Self {
+        Self {
+            value: self.value.saturating_sub(n.value),
+            _marker: PhantomData,
+        }
+    }
+
+    pub fn zero() -> Self {
+        Self::new(0)
+    }
+
+    pub fn is_zero(&self) -> bool {
+        self.value == 0
+    }
+}
+
+impl<T> TypedPoint<T> {
+    pub fn new(row: u32, column: u32) -> Self {
+        Self {
+            value: Point::new(row, column),
+            _marker: PhantomData,
+        }
+    }
+
+    pub fn wrap(point: Point) -> Self {
+        Self {
+            value: point,
+            _marker: PhantomData,
+        }
+    }
+
+    pub fn row(&self) -> u32 {
+        self.value.row
+    }
+
+    pub fn column(&self) -> u32 {
+        self.value.column
+    }
+
+    pub fn zero() -> Self {
+        Self::wrap(Point::zero())
+    }
+
+    pub fn is_zero(&self) -> bool {
+        self.value.is_zero()
+    }
+}
+
+impl<T> TypedRow<T> {
+    pub fn new(row: u32) -> Self {
+        Self {
+            value: row,
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<T> Copy for TypedOffset<T> {}
+impl<T> Copy for TypedPoint<T> {}
+impl<T> Copy for TypedRow<T> {}
+
+impl<T> Clone for TypedOffset<T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+impl<T> Clone for TypedPoint<T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+impl<T> Clone for TypedRow<T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<T> Default for TypedOffset<T> {
+    fn default() -> Self {
+        Self::new(0)
+    }
+}
+impl<T> Default for TypedPoint<T> {
+    fn default() -> Self {
+        Self::wrap(Point::default())
+    }
+}
+impl<T> Default for TypedRow<T> {
+    fn default() -> Self {
+        Self::new(0)
+    }
+}
+
+impl<T> PartialOrd for TypedOffset<T> {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.value.cmp(&other.value))
+    }
+}
+impl<T> PartialOrd for TypedPoint<T> {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.value.cmp(&other.value))
+    }
+}
+impl<T> PartialOrd for TypedRow<T> {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.value.cmp(&other.value))
+    }
+}
+
+impl<T> Ord for TypedOffset<T> {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.value.cmp(&other.value)
+    }
+}
+impl<T> Ord for TypedPoint<T> {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.value.cmp(&other.value)
+    }
+}
+impl<T> Ord for TypedRow<T> {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.value.cmp(&other.value)
+    }
+}
+
+impl<T> PartialEq for TypedOffset<T> {
+    fn eq(&self, other: &Self) -> bool {
+        self.value == other.value
+    }
+}
+impl<T> PartialEq for TypedPoint<T> {
+    fn eq(&self, other: &Self) -> bool {
+        self.value == other.value
+    }
+}
+impl<T> PartialEq for TypedRow<T> {
+    fn eq(&self, other: &Self) -> bool {
+        self.value == other.value
+    }
+}
+
+impl<T> Eq for TypedOffset<T> {}
+impl<T> Eq for TypedPoint<T> {}
+impl<T> Eq for TypedRow<T> {}
+
+impl<T> Debug for TypedOffset<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}Offset({})", type_name::<T>(), self.value)
+    }
+}
+impl<T> Debug for TypedPoint<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "{}Point({}, {})",
+            type_name::<T>(),
+            self.value.row,
+            self.value.column
+        )
+    }
+}
+impl<T> Debug for TypedRow<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}Row({})", type_name::<T>(), self.value)
+    }
+}
+
+impl<T> Display for TypedOffset<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        Display::fmt(&self.value, f)
+    }
+}
+impl<T> Display for TypedRow<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        Display::fmt(&self.value, f)
+    }
+}
+
+fn type_name<T>() -> &'static str {
+    std::any::type_name::<T>().split("::").last().unwrap()
+}
+
+impl<T> Add<TypedOffset<T>> for TypedOffset<T> {
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self {
+        TypedOffset::new(self.value + other.value)
+    }
+}
+impl<T> Add<TypedPoint<T>> for TypedPoint<T> {
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self {
+        TypedPoint::wrap(self.value + other.value)
+    }
+}
+
+impl<T> Sub<TypedOffset<T>> for TypedOffset<T> {
+    type Output = Self;
+    fn sub(self, other: Self) -> Self {
+        TypedOffset::new(self.value - other.value)
+    }
+}
+impl<T> Sub<TypedPoint<T>> for TypedPoint<T> {
+    type Output = Self;
+    fn sub(self, other: Self) -> Self {
+        TypedPoint::wrap(self.value - other.value)
+    }
+}
+
+impl<T> AddAssign<TypedOffset<T>> for TypedOffset<T> {
+    fn add_assign(&mut self, other: Self) {
+        self.value += other.value;
+    }
+}
+impl<T> AddAssign<TypedPoint<T>> for TypedPoint<T> {
+    fn add_assign(&mut self, other: Self) {
+        self.value += other.value;
+    }
+}
+
+impl<T> SubAssign<Self> for TypedOffset<T> {
+    fn sub_assign(&mut self, other: Self) {
+        self.value -= other.value;
+    }
+}
+impl<T> SubAssign<Self> for TypedRow<T> {
+    fn sub_assign(&mut self, other: Self) {
+        self.value -= other.value;
+    }
+}