[A11y][Keyboard shortcuts] Add bugfix flag for magnifying dialog

* This adds a bugfix flag for magnifying the confirmation dialog for the
  Magnification key gesture.
* This is related to a bugfix for the work flagged by
  enable_talkback_and_magnifier_key_gestures.

Bug: 425722546
Flag: com.android.hardware.input.enable_magnify_magnification_key_gesture_dialog
Flag: com.android.hardware.input.enable_talkback_and_magnifier_key_gestures
Test: N/A, adding flag
Change-Id: Ia70e098f2053d3f2db10028eb913d73954e56af7