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/src/db/tables/worktree_repository_statuses.rs

@@ -12,11 +12,26 @@ pub struct Model {
     pub work_directory_id: i64,
     #[sea_orm(primary_key)]
     pub repo_path: String,
+    /// Old single-code status field, no longer used but kept here to mirror the DB schema.
     pub status: i64,
+    pub status_kind: StatusKind,
+    /// For unmerged entries, this is the `first_head` status. For tracked entries, this is the `index_status`.
+    pub first_status: Option<i32>,
+    /// For unmerged entries, this is the `second_head` status. For tracked entries, this is the `worktree_status`.
+    pub second_status: Option<i32>,
     pub scan_id: i64,
     pub is_deleted: bool,
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq, EnumIter, DeriveActiveEnum)]
+#[sea_orm(rs_type = "i32", db_type = "Integer")]
+pub enum StatusKind {
+    Untracked = 0,
+    Ignored = 1,
+    Unmerged = 2,
+    Tracked = 3,
+}
+
 #[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
 pub enum Relation {}