feat(MultiFingerMultiTap): Add two-finger triple-tap shortcut on magnification dialog

The shortcut is separate from single-finger triple-tap. It’s under hardware shortcut and above/outside of Advanced section.

Bug: 297805269
Test: manual
Test: atest ToggleScreenMagnificationPreferenceFragmentTest
Change-Id: Id74cf3e457c04e167f3100d977b6c70c5d601026