fix(deep): Add intent actions for a11y magnification & flash notif pages

This aligns these accessibility system feature settings pages with other
similar pages, allowing an external caller to launch this page by
sending an intent.

Similar to other accessibility system settings neither page is protected
by a permission since these settings provide no avenue for abuse.

Bug: 388304424
Test: adb shell am start -W -a android.settings.MAGNIFICATION_SETTINGS;
      Observe that the Magnification Settings page is opened.
Test: adb shell am start -W -a android.settings.FLASH_NOTIFICATIONS_SETTINGS;
      Observe that the Flash Notifications Settings page is opened.
Flag: EXEMPT low risk manifest change
Change-Id: Ibe9e1031f30416c5f3fcfb7ae2fe76e8dcd45714