Don't show notification guts in kiosk mode

If the device is determined to be in kiosk mode (specifically, LOCK_TASK_MODE_LOCKED), it should not be permitted to modify notification settings. This only applies to the fully locked state and not to app pinning (LOCK_TASK_MODE_PINNED).

Bug: 424876676
Test: NotificationGutsManagerTest, manual verification that guts could not open
Flag: EXEMPT bug fix
Change-Id: I1423a8c2d29055b31fc8c7fce8c574e1c19c4841