Add stress tests for MediaProviderTranscode tests

We add 2 tests:
one reads a modern file of a few seconds duration a hundred times.
second reads a modern files of ~25 seconds duration 20 times.

The idea is to have one package cause multiple transcodings
concurrently, and in the process try to stress the system.

BUG: 169546642
Test: cts-tradefed run cts-dev --module MediaProviderTranscode
Change-Id: I64086ad2ff4ec6e1c299b4e74ba9ec39f633b982
3 files changed