Renamed and moved InputWindow and related files

In preparation for the hierarchy listener interface, moved the
InputWindow structs into libgui and have libinput dependant on libgui.
Also renamed InputWindow to exclude Input since it will be used for more
generic purposes.

Test: Builds and flashes
Bug: 188792659

Change-Id: I24262cbc14d409c00273de0024a672394a959e5f