Add a setting to control the number of context lines in excerpts (#37138)

Fixes https://github.com/zed-industries/zed/discussions/28739

Release Notes:

- Added a setting, `excerpt_context_lines`, for setting the number of
context lines shown in a multibuffer

crates/git_ui/src/commit_view.rs

@@ -1,6 +1,6 @@
 use anyhow::{Context as _, Result};
 use buffer_diff::{BufferDiff, BufferDiffSnapshot};
-use editor::{Editor, EditorEvent, MultiBuffer, SelectionEffects};
+use editor::{Editor, EditorEvent, MultiBuffer, SelectionEffects, multibuffer_context_lines};
 use git::repository::{CommitDetails, CommitDiff, CommitSummary, RepoPath};
 use gpui::{
     AnyElement, AnyView, App, AppContext as _, AsyncApp, Context, Entity, EventEmitter,
@@ -195,7 +195,7 @@ impl CommitView {
                             PathKey::namespaced(FILE_NAMESPACE, path),
                             buffer,
                             diff_hunk_ranges,
-                            editor::DEFAULT_MULTIBUFFER_CONTEXT,
+                            multibuffer_context_lines(cx),
                             cx,
                         );
                         multibuffer.add_diff(buffer_diff, cx);