Make RemoteInputConnectionImpl package-private

This CL mechanically moves RemoteInputConnectionImpl from

  com.android.internal.inputmethod

to

  android.view.inputmethod

just to make it a package-private class, as it is (and should be) used
only by InputMethodManager.

This is a mechanical refactoring.  There must be no developer
observable behavior change in this CL.

Bug: 192412909
Test: presubmit
Change-Id: I2d9bd4a5cb39d506a70331c9c930a74580cdbfa0