Re-enable IME image inserting for RemoteInputView

The prior implementation was not calling
InputContentInfo#requestPermission, resulting in the Uri for the image
from the IME not being accessible by SysUI. This is because when using
the InputConnectionCompat utils from AndroidX, the caller needs to
explicitly invoke that method, which we were not doing.

In general, it is preferred that SystemUI does not depend on the
support lib when possible, so this change re-implements the IME image
insertion handing using the built-in mechanism, which also
automatically handles granting the appropriate URI permissions for
SystemUI.

Bug: 163595585
Test: manual, atest
Change-Id: I473a03f3e5a1d756eb4b083d52bd992839911c66