Pull action_log into its own crate (#35959)

Release Notes:

- N/A

crates/agent_ui/src/agent_diff.rs

@@ -1,9 +1,9 @@
 use crate::{Keep, KeepAll, OpenAgentDiff, Reject, RejectAll};
 use acp_thread::{AcpThread, AcpThreadEvent};
+use action_log::ActionLog;
 use agent::{Thread, ThreadEvent, ThreadSummary};
 use agent_settings::AgentSettings;
 use anyhow::Result;
-use assistant_tool::ActionLog;
 use buffer_diff::DiffHunkStatus;
 use collections::{HashMap, HashSet};
 use editor::{