Added writer fuzzers

Test: ./amrnb_writer_fuzzer
Test: ./amrwb_writer_fuzzer
Test: ./mpeg4_writer_fuzzer
Test: ./ogg_writer_fuzzer
Test: ./webm_writer_fuzzer
Bug: 173672210
Bug: 173672657
Bug: 173672212
Bug: 173672344

Change-Id: I742a493bb1409e52c56060c896b36890a8238a51