Move up user verifications in startInputOrWindowGainedFocus

Move up user running and user switching verification.

This CL is a preparation for FocusController. It moves up the user
running and user switching verifications. This refactoring will
make the moving startInput logic to FocusController easier.

This is just a refactoring CL, no behavior change is expected.

Bug: 314150112
Test: atest CtsInputMethodTestCases FrameworksServicesTests
Change-Id: I733a8fc813d751c8529a15d5800476af4a61c3dd