Ensure focus_in and focus_out fire on window activation (#3993)

Also:
- Rename cx.on_blur to cx.on_focus_lost
- Fix a bug where notify calls in focus handlers were ignored
- Fix a bug where vim would get stuck in the wrong mode when switching
  windows

Release Notes:

- (preview only) vim: fix switching between multiple windows

crates/workspace/src/workspace.rs

@@ -537,7 +537,7 @@ impl Workspace {
         })
         .detach();
 
-        cx.on_blur_window(|this, cx| {
+        cx.on_focus_lost(|this, cx| {
             let focus_handle = this.focus_handle(cx);
             cx.focus(&focus_handle);
         })