Enforce VirtualTouchscreen dimensions are positive

Adds an IllegalArgumentException to the implementation of
createVirtualTouchscreen if the dimension has one or two non positive
components. Without this check the native layer silently fails (only a
warning is printed in the logs). The creation of the VirtualTouchscreen
looks successful because the DeviceCretionException does not get passed
past the Binder call. When the first VirtualTouchEvent is sent to the
VirtualTouchscreen the sendTouchEvent() method throws an exception
because it can't find the underlying input device descriptor.

Bug: 259554911
Test: atest FrameworksServicesTests:VirtualDeviceManagerServiceTest
Change-Id: I085b8822d0f364b49060404480795626554fc155