Simplify IMMS#startInputOrWindowGainedFocusInternal() part 5/5

This is a series of CLs to reduce the average indentation level of
InputMethodManagerService#startInputOrWindowGainedFocusInternal().

This CL does several format clean-ups and fixes several lint errors.

This is a mechanical refactoring.  There should be no behavior change.

Bug: 34886274
Test: atest CtsInputMethodTestCases CtsInputMethodServiceHostTestCases
Change-Id: Icd5b7da96e1ec11b329e2d1a4a885796510e23f9