acp: Clean up entry views on rewind (#36197)

We were leaking diffs and terminals on rewind, we'll now clean them up.
This PR also introduces a refactor of how we mantain the entry view
state to use a `Vec` that's kept in sync with the thread entries.

Release Notes:

- N/A

crates/agent_servers/src/acp/v1.rs

@@ -111,7 +111,7 @@ impl AgentConnection for AcpConnection {
         self: Rc<Self>,
         project: Entity<Project>,
         cwd: &Path,
-        cx: &mut AsyncApp,
+        cx: &mut App,
     ) -> Task<Result<Entity<AcpThread>>> {
         let conn = self.connection.clone();
         let sessions = self.sessions.clone();