Created a dedicated activity for EditShortcutsPreferenceFragment.

This will allow it to be reached via intent.

Test: Send an intent with the ACCESSIBILITY_SHORTCUT_SETTINGS action (make sure the "targets" fragment argument is populated with a string array of shortcut targets)
Flag: None (Change adds definitions but no new behavior)
Bug: 297583708
Change-Id: Ie0dd4918a4f38c04b781308f170b568af30bb238