Kepp PreviewDataProvider instace over a configuration change

Add a view model, PreviewViewModel, to retain a PreviewDataProvider
instance.
Tangentally, move ChooserActivity#isImageType method into
MimeTypeClassifier (to avoid keep a link to the activity).

Fix: 281929002
Test: manual testing, vierify through injected debug logging that the
 object is not re-created.
Change-Id: I7be397089ca33e589a3ecbd6012929bfe3c5433a
8 files changed