Remove dependency on IWindowManager from InputMethodBindingController

With this CL,

  InputMethodBindingController

starts using

  WindowManagerInternal#addWindowToken()

instead of

  IWindowManager#addWindowToken()

for simplicity.

There should be no observable behavior change in this CL.

Bug: 234882948
Test: presubmit
Change-Id: Ib93d0c2b9a9580bbf1d25dda2a044741c265a0b5