Use USER_LIFECYCLE_EVENT_TYPE_SWITCHING to detect user switched event.

SWITCHING and SWITCHED would be sent consecutively on the same thread,
and so creating a USER_LIFECYCLE_EVENT_TYPE_SWITCHED event has been
determined to be redundant.

See b/153745017 for more details.

Bug: 153379372
Test: Manual
Change-Id: Iaabb7a8b31f7a5e4a46cbe4d7ea683b06756404e