Refactored libstagefright_mediamuxer_fuzzer

The following are updates to the fuzzer:
1. Resolved a fuzzer error.
2. Added new APIs.
3. Added an enum for relevant values.
4. Randomized parameter values.
5. Integrated meta data population functionality
   from MediaMuxerFuzzer.h into MediaMuxerFuzzer.cpp,
   rendering the header file redundant and removing it.
6. Code coverage improved from 59.22% to 95.63%.

Test: ./libstagefright_mediamuxer_fuzzer
exec/s: 404
Bug: 331540179

Change-Id: I67ff65994e26328b5d64275ee8bd8bfd70975e3a