Partly inline IMMS#attachNewAccessibilityLocked()

This CL partly inlines

  InputMethodManagerService#attachNewAccessibilityLocked(),

which was added to as part of our A11yIme effort [1].

This CL is a mechanical refactoring and changes nothing.

 [1]: Ia651a811093a939d00c081be1961e24ed3ad0356
      fb17e5ae

Bug: 234882948
Test: presubmit
Change-Id: I52e174433df6476ef1d2126e4fdbd18142aaf24a