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/collab/migrations.sqlite/20221109000000_test_schema.sql

@@ -112,6 +112,9 @@ CREATE TABLE "worktree_repository_statuses" (
     "work_directory_id" INT8 NOT NULL,
     "repo_path" VARCHAR NOT NULL,
     "status" INT8 NOT NULL,
+    "status_kind" INT4 NOT NULL,
+    "first_status" INT4 NULL,
+    "second_status" INT4 NULL,
     "scan_id" INT8 NOT NULL,
     "is_deleted" BOOL NOT NULL,
     PRIMARY KEY(project_id, worktree_id, work_directory_id, repo_path),