Add `enableShortcutTypeForTargets` method in the A11yManager

Bug: 317424693
Test: manual (modify Settings app to use this new method, and toggle the
shortcut options in the Settings app)
Test: atest AccessibilityManagerServiceTest
Test: atest AccessibilityManagerTest
Test: atest AccessibilityUtilsTest

Flag: N/A the caller should call this method behind a flag
NO_IFTTT=New IFTTT tags

Change-Id: I6e6405ab16d693b4344e565824bf2ad4c18da002