debugger: Extract running state from DebugSession mode and remove mode field (#29646)

DebugSession.mode is no longer needed because project::debugger::Session
manages its own state now (booting, running, terminated), and removing
mode simplifies a lot of the code that uses running state.

I used Zed AI to do a good chunk of the refactor, but I doubled-checked
everything it did and changed a good amount of its updates.

Release Notes:

- N/A

Co-authored-by: Zed AI <ai@zed.dev>

crates/debugger_ui/src/tests/console.rs

@@ -87,10 +87,7 @@ async fn test_handle_output_event(executor: BackgroundExecutor, cx: &mut TestApp
     let running_state =
         active_debug_session_panel(workspace, cx).update_in(cx, |item, window, cx| {
             cx.focus_self(window);
-            item.mode()
-                .as_running()
-                .expect("Session should be running by this point")
-                .clone()
+            item.running_state().clone()
         });
 
     cx.run_until_parked();
@@ -105,7 +102,7 @@ async fn test_handle_output_event(executor: BackgroundExecutor, cx: &mut TestApp
 
             assert_eq!(
                 "First console output line before thread stopped!\nFirst output line before thread stopped!\n",
-                active_debug_session_panel.read(cx).mode().as_running().unwrap().read(cx).console().read(cx).editor().read(cx).text(cx).as_str()
+                active_debug_session_panel.read(cx).running_state().read(cx).console().read(cx).editor().read(cx).text(cx).as_str()
             );
         })
         .unwrap();
@@ -154,7 +151,7 @@ async fn test_handle_output_event(executor: BackgroundExecutor, cx: &mut TestApp
 
             assert_eq!(
                 "First console output line before thread stopped!\nFirst output line before thread stopped!\nSecond output line after thread stopped!\nSecond console output line after thread stopped!\n",
-                active_session_panel.read(cx).mode().as_running().unwrap().read(cx).console().read(cx).editor().read(cx).text(cx).as_str()
+                active_session_panel.read(cx).running_state().read(cx).console().read(cx).editor().read(cx).text(cx).as_str()
             );
         })
         .unwrap();