Fix accesses to InputMethodMenuController#mSettings without lock

This CL fixes an existing issue that

  InputMethodMenuController#mSettings

gets accessed without acquiring ImfLock.class.

While it's OK to access

  InputMethodMenuController#mWindowManagerInternal

and its methods without acquiring ImfLock.class, mSettings isn't
because it's still a mutable object that can change at any time.

Bug: 309868254
Test: presubmit
Change-Id: Id3108004d9f120a51cc28fe53321f6c62bd0b16a