Add "android.software.preview_sdk" feature

Conditionally add the "android.software.preview_sdk" feature to any
targets that have a Build.VERSION.CODENAME != "REL". This allows clients
to filter out platforms that are not running official Android releases.

Bug: 31064561
Test: verified using PackageManager#getSystemAvailableFeatures()
Change-Id: I539e9537f5f9a572db0a15489b14710e2e8eb0c0
1 file changed