isMobileMagnifierVisible static method
Returns true if a mobile magnifier is currently visible, or false if it's
not.
The mobile magnifier looks different for iOS and Android. The magnifier also follows different focal points depending on whether it's iOS or Android. But in both cases, a magnifier is a small shape near the user's finger or selection, which shows the editor content at an enlarged/magnified level.
This method doesn't take a superEditorFinder because the magnifier is displayed
in the application overlay, and is therefore completely independent from the
SuperEditor subtree. There's no obvious way to associate a magnifier with
a specific SuperEditor.
See also: wantsMobileMagnifierToBeVisible
Implementation
static bool isMobileMagnifierVisible() {
  return find.byKey(DocumentKeys.magnifier).evaluate().isNotEmpty;
}