add MediaCodec XML minsdk=# attribute

Add a minsdk="#" attribute to the MediaCodec XML clause. This supports
the idea of a codec distributed via mainline but enabled only on certain
Android releases.

Bug: 242057615
Test: enable/minsdk combinations on Q/R/S/T/master devices
Test: atest XMLParserTest
Change-Id: I708aa6dcd49cf06fdab011e6611551c482027ebf