Introduce DisplayRow, MultiBufferRow newtypes and BufferRow type alias (#11656)

Part of https://github.com/zed-industries/zed/issues/8081

To avoid confusion and bugs when converting between various row `u32`'s,
use different types for each.
Further PRs should split `Point` into buffer and multi buffer variants
and make the code more readable.

Release Notes:

- N/A

---------

Co-authored-by: Piotr <piotr@zed.dev>

crates/git/src/diff.rs

@@ -30,18 +30,6 @@ pub struct DiffHunk<T> {
     pub diff_base_byte_range: Range<usize>,
 }
 
-impl DiffHunk<u32> {
-    pub fn status(&self) -> DiffHunkStatus {
-        if self.diff_base_byte_range.is_empty() {
-            DiffHunkStatus::Added
-        } else if self.associated_range.is_empty() {
-            DiffHunkStatus::Removed
-        } else {
-            DiffHunkStatus::Modified
-        }
-    }
-}
-
 impl sum_tree::Item for DiffHunk<Anchor> {
     type Summary = DiffHunkSummary;