Fix CSLs with alpha attribute in AppCompat

AppCompat supports themeable CSLs from API 24
onwards, but certain attributes were only added
in API 11 such as android:alpha. To workaround this
we add the app:alpha attribute to allow us to set it
on earlier API levels.

AppCompat also just lets the framework handle themeable
CSLs on API 23, so our CSLs which only set app:alpha
don't actually work very well on API 23+, since it the
framework doesn't know about app:alpha.

Fixed by double setting the attribute.

BUG: 27867013
Change-Id: Ia97c287aaa809b5048724a4610082920a16aea26
8 files changed