Disables warning dialog when hardware shortcut enabled on purpose

If AccessibilityManager is called to enable a hardware shortcut,
it will turn off the first-time warning dialog for using the shortcut

(This change also replaces instances of RequresFlagsEnabled/Disabled
with Enable/DisableFlags in AccessibilityManagerServiceTest)

Test: atest AccessibilityManagerServiceTest
Flag: aconfig enable_hardware_shortcut_disables_warning
Bug: 287065325
Change-Id: Ic60bf3c73c6be1f6c6477430349fb9d4a8d74358