Port recent_projects to Zed2 (#3525)

This PR ports the `recent_projects` crate to Zed2 (`recent_projects2`).

Absent from this PR is wiring up the "Recent Projects" item in the title
bar. We'll come back to that soon.

Release Notes:

- N/A

crates/workspace2/src/workspace2.rs

@@ -45,9 +45,10 @@ use node_runtime::NodeRuntime;
 use notifications::{simple_message_notification::MessageNotification, NotificationHandle};
 pub use pane::*;
 pub use pane_group::*;
+use persistence::DB;
 pub use persistence::{
     model::{ItemId, SerializedWorkspace, WorkspaceLocation},
-    WorkspaceDb, DB,
+    WorkspaceDb, DB as WORKSPACE_DB,
 };
 use postage::stream::Stream;
 use project::{Project, ProjectEntryId, ProjectPath, Worktree, WorktreeId};