Extract out logic from IMMS#getCurrentInputMethodSubtypeLocked()

This is a mechanical refactoring CL to extract out a bit complicated
logic out of

  InputMethodManagerService#getCurrentInputMethodSubtypeLocked()

without changing any behavior.

Bug: 346658341
Test: presubmit
Flag: EXEMPT refactor
Change-Id: Ie876f94d3877370b88f2d605877d3b45c0a63e2b
2 files changed