Tuner HAL VTS: Testing LnbDescrambling

This CL implements integration tests for LnbDescrambling. The new
testing function ScrambledBroadcastTestWithLnb tests the functionality
of the Lnb and, if the frontend is not software, tests passing a signal
through the tuner and descrambling a broadcast.

Additionally, this CL adds a context variable to the
ScrambledBroadcastTest function to determine which dataflow
(LnbDescrambling or Descrambling) is being tested. It specializes
behavior differently for each datflow to model real world
use cases. Notably, a Descrambler could be tested with no frontend when
playing back a descrambled recording, whereas testing an Lnb broadcast
would require a hardware frontend.

Bug: b/240476983

Test: ts-tradefed run vts --module VtsHalTvTunerTargetTest
Change-Id: Ia35d2d45dca4411b0a15f0585d6ddaecd3f9321a