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/project/src/task_store.rs

@@ -12,7 +12,7 @@ use language::{
 use rpc::{proto, AnyProtoClient, TypedEnvelope};
 use settings::{watch_config_file, SettingsLocation};
 use task::{TaskContext, TaskVariables, VariableName};
-use text::BufferId;
+use text::{BufferId, OffsetRangeExt};
 use util::ResultExt;
 
 use crate::{
@@ -125,12 +125,10 @@ impl TaskStore {
                         .filter_map(|(k, v)| Some((k.parse().log_err()?, v))),
                 );
 
-                for range in location
-                    .buffer
-                    .read(cx)
-                    .snapshot()
-                    .runnable_ranges(location.range.clone())
-                {
+                let snapshot = location.buffer.read(cx).snapshot();
+                let range = location.range.to_offset(&snapshot);
+
+                for range in snapshot.runnable_ranges(range) {
                     for (capture_name, value) in range.extra_captures {
                         variables.insert(VariableName::Custom(capture_name.into()), value);
                     }