MediaExtractorTest: Do not mandate DTS support in extractors

Since support for extracting DTS in MPEG2-TS is not mandatory,
the tests are now updated to assert on mediaType and trackCount
only if the extractor is able to identify a track.

Also, the tests now validate media type for devices running
Android T and above.

Bug: 289014964
Test: atest CtsMediaExtractorTestCases
(cherry picked from https://android-review.googlesource.com/q/commit:0d006f834405910c14153960509b32a2263ec7b5)
Merged-In: I37b28739ef600e1db3faaa4679b3d66525b7f011
Change-Id: I37b28739ef600e1db3faaa4679b3d66525b7f011