Fix window double borrows (#23739)

Fix bugs caused by the window context PR, where the window could be on
the stack and is then requested from the App.
This PR also adds derive macros for `AppContext` and `VisualContext` so
that it's easy to define further contexts in API code, such as
`editor::BlockContext`.

Release Notes:

- N/A

crates/zed/src/zed.rs

@@ -1200,8 +1200,7 @@ fn show_keymap_file_json_error(
                     cx.emit(DismissEvent);
                 })
         })
-    })
-    .log_err();
+    });
 }
 
 fn show_keymap_file_load_error(
@@ -1245,7 +1244,6 @@ fn show_keymap_file_load_error(
                     })
                 })
             })
-            .log_err();
         })
         .ok();
     })