THEMES-177: Added Java API to temporarily manipulate activity configChanges.

This hack is designed to avoid adding a new flag value to
attrs_manifest.xml for "theme" configChange, which will add a new R.id
value and destabalize aapt's enumeration.  Not a perfect replacement
however as modifying the ActivityInfo in this way only applies to the
current Activity instance.  Other components querying the PackageManager
would not see the revised configChanges value, nor would a separate
instance of the same Activity.

CR: Dirk Sigurdson
CR: Ed Carrigan