Add PROPERTY_MEDIA_CAPABILITIES API

This string allows apps add a media_capabilities.xml resource to the
AndroidManifest.xml

The media_capabilities.xml file will in turn allow apps declare the
media capabilities they support, so the OS can transcode unsupported
formats to compatible formats for the app

Note, that the hard-coded string is already in use in MediaProvider
and is covered by TranscodeTest mentioned below

Test: atest TranscodeTest
Bug: 178187121
Change-Id: I46cfaefe8fb7f0bbd14896efdee61dcc4da19783