Issue #44631).

This mechanism has been replaced by making MouseRegion
a stateful widget, so that it can perform the mounted-exit
check by itself by blocking the callback when unmounted.
Therefore, these methods have been removed, and MouseTracker
no longer tracks all annotations on the screen.

Description of change

The MouseTracker class has removed three methods related
to attaching annotations:

void attachAnnotation(MouseTrackerAnnotation annotation) {/* ... */}

void detachAnnotation(MouseTrackerAnnotation annotation) {/* ... */}

@visibleForTesting
-  bool isAnnotationAttached(MouseTrackerAnnotation annotation) {/* ... */}
 }

RenderMouseRegion and MouseTrackerAnnotation no longer perform the
mounted-exit check, while MouseRegion still does.

Migration guide

Calls to MouseTracker.attachAnnotation and
detachAnnotation should be removed with little to no impact: