Fix headsup notification RemoteInputView appearance animation

This CL fixes a bug where the appearance animation of the RemoteInputView in a headsup collapsed notification was slightly broken. The RemoteInputView would do its appearance animation partly outside (below) the notification boundaries. This was because the RemoteInputView was prevented to overlap the hint during the expand animation.

Bug: 174148361
Test: atest RemoteInputViewTest, Manual, i.e. posting various types of Notifications from the Notify2-RVC application with a reply action added to them. Then observing the animations visually and analyzing frames from screen recordings.
Change-Id: I90a637e9b57dea0e365699cef9e088a562301f55