Allow viewing past commits in Zed (#27636)

This PR adds functionality for loading the diff for an arbitrary git
commit, and displaying it in a tab. To retrieve the diff for the commit,
I'm using a single `git cat-file --batch` invocation to efficiently load
both the old and new versions of each file that was changed in the
commit.

Todo

* Features
* [x] Open the commit view when clicking the most recent commit message
in the commit panel
  * [x] Open the commit view when clicking a SHA in a git blame column
  * [x] Open the commit view when clicking a SHA in a commit tooltip
  * [x] Make it work over RPC
  * [x] Allow buffer search in commit view
* [x] Command palette action to open the commit for the current blame
line
* Styling
* [x] Add a header that shows the author, timestamp, and the full commit
message
  * [x] Remove stage/unstage buttons in commit view
  * [x] Truncate the commit message in the tab
* Bugs
  * [x] Dedup commit tabs within a pane
  * [x] Add a tooltip to the tab

Release Notes:

- Added the ability to show past commits in Zed. You can view the most
recent commit by clicking its message in the commit panel. And when
viewing a git blame, you can show any commit by clicking its sha.

crates/proto/src/proto.rs

@@ -340,6 +340,8 @@ messages!(
     (ListRemoteDirectoryResponse, Background),
     (ListToolchains, Foreground),
     (ListToolchainsResponse, Foreground),
+    (LoadCommitDiff, Foreground),
+    (LoadCommitDiffResponse, Foreground),
     (LspExtExpandMacro, Background),
     (LspExtExpandMacroResponse, Background),
     (LspExtOpenDocs, Background),
@@ -534,6 +536,7 @@ request_messages!(
     (JoinRoom, JoinRoomResponse),
     (LeaveChannelBuffer, Ack),
     (LeaveRoom, Ack),
+    (LoadCommitDiff, LoadCommitDiffResponse),
     (MarkNotificationRead, Ack),
     (MoveChannel, Ack),
     (OnTypeFormatting, OnTypeFormattingResponse),
@@ -668,6 +671,7 @@ entity_messages!(
     JoinProject,
     LeaveProject,
     LinkedEditingRange,
+    LoadCommitDiff,
     MultiLspQuery,
     RestartLanguageServers,
     OnTypeFormatting,