Refine {SHOW,HIDE}_MY_SOFT_INPUT constants

Naming of SoftInputShowHideReason#{SHOW,HIDE}_MY_SOFT_INPUT
constants may not clear enough to indicate its semantics.

Improve show/hide reasons of InputMethodService by:

-. Update constants naming to {SHOW,HIDE}_SOFT_INPUT_FROM_IME.
-. Introduce respective reasons to indicate different hide request
   cases within IME process.

Bug: 224565148
Test: presubmit
Test: atest CtsInputMethodTestCases and observe logs
Change-Id: I8b148e9b5ab05ff7b827c6b8fe23008ca30a8c4b