Move IME token validation to privilegedOperations

This moves all the IME token validation from methods in IMMS to the
actual callers in InputMethodPrivilegedOperationsImpl, ensuring all the
validation happens in the same place.

Due to this, the privilegedOperations methods now acquire the ImfLock,
and call into IMMS with the lock held, which is equivalent to the way
the lock was being acquired before, inside the called IMMS methods.

Flag: EXEMPT refactor
Test: atest and checking logcat
Bug: 355154964
Change-Id: I322ae7dbca9c1bb33fdb4992b44b9676bba4abd9