Async startInputOrWindowGainedFocus

We ignore the result if startInputReason is
WINDOW_FOCUS_GAIN_REPORT_WITH_CONNECTION or
WINDOW_FOCUS_GAIN_REPORT_WITHOUT_CONNECTION
in startInputOrWindowGainedFocus.

Introduce USE_REPORT_WINDOW_GAINED_FOCUS_ASYNC
flag to control following behavior:

-. Don't wait the result if it only report the
   focus gain. Have another IPC for this case
   to prevent the UI thread be blocked.

-. Throw the exception to the client side if it
   happened.

Bug: 185928120
Test: atest CtsInputMethodTestCases
Change-Id: Ic584203c1221fbae17f5e2d8f09e3992df061646