Make Property objects in View final

The various Properties added to View in 4.0 (ALPHA, TRANSLATION_X, etc.)
were not final, making it possible to assign on property to another.
Not something that someone would want to do, but we should try to prevent
that kind of mess. This API change makes those properties final.

Change-Id: I7d0c7f738eb2074d0781b1ba6a7c19339bac4477