This PR created a main page for platform view tests in the android views testing app. The main page none contains a list of the links to the pages being tested. It puts the android view motion events tests to a sub page.
The PR also added iOS related files to get ready for adding the iOS platform views tests.

The test places an embedded Android view at the top left, and verifies
that motion events that get to FlutterView are equivalent to the
synthesized motion events that gets to the embedded view.

See the README.md for more high level details.