Represent git statuses more faithfully (#23082)

First, parse the output of `git status --porcelain=v1` into a
representation that can handle the full "grammar" and doesn't lose
information.

Second, as part of pushing this throughout the codebase, expand the use
of the existing `GitSummary` type to all the places where status
propagation is in play (i.e., anywhere we're dealing with a mix of files
and directories), and get rid of the previous `GitSummary ->
GitFileStatus` conversion.

- [x] Synchronize new representation over collab
  - [x] Update zed.proto
  - [x] Update DB models
- [x] Update `GitSummary` and summarization for the new `FileStatus`
- [x] Fix all tests
  - [x] worktree
  - [x] collab
- [x] Clean up `FILE_*` constants
- [x] New collab tests to exercise syncing of complex statuses
- [x] Run it locally and make sure it looks good

Release Notes:

- N/A

---------

Co-authored-by: Mikayla <mikayla@zed.dev>
Co-authored-by: Conrad <conrad@zed.dev>

crates/proto/proto/zed.proto

@@ -1784,7 +1784,9 @@ message RepositoryEntry {
 
 message StatusEntry {
     string repo_path = 1;
-    GitStatus status = 2;
+    // Can be removed once collab's min version is >=0.171.0.
+    GitStatus simple_status = 2;
+    GitFileStatus status = 3;
 }
 
 enum GitStatus {
@@ -1792,6 +1794,31 @@ enum GitStatus {
     Modified = 1;
     Conflict = 2;
     Deleted = 3;
+    Updated = 4;
+    TypeChanged = 5;
+    Renamed = 6;
+    Copied = 7;
+    Unmodified = 8;
+}
+
+message GitFileStatus {
+    oneof variant {
+        Untracked untracked = 1;
+        Ignored ignored = 2;
+        Unmerged unmerged = 3;
+        Tracked tracked = 4;
+    }
+
+    message Untracked {}
+    message Ignored {}
+    message Unmerged {
+        GitStatus first_head = 1;
+        GitStatus second_head = 2;
+    }
+    message Tracked {
+        GitStatus index_status = 1;
+        GitStatus worktree_status = 2;
+    }
 }
 
 message BufferState {