Reorganize source files of collab::db

* Move all sea_orm tables into a 'tables' module
* Move TestDb into its own file
* Move id types into their own module

crates/collab/src/db/tables.rs

@@ -0,0 +1,20 @@
+pub mod access_token;
+pub mod channel;
+pub mod channel_member;
+pub mod channel_path;
+pub mod contact;
+pub mod follower;
+pub mod language_server;
+pub mod project;
+pub mod project_collaborator;
+pub mod room;
+pub mod room_participant;
+pub mod server;
+pub mod signup;
+pub mod user;
+pub mod worktree;
+pub mod worktree_diagnostic_summary;
+pub mod worktree_entry;
+pub mod worktree_repository;
+pub mod worktree_repository_statuses;
+pub mod worktree_settings_file;