Refactor imagedecoder_fuzzer

The following are updates to the fuzzer:
1. Added new APIs and randomized API calls.
2. Coverage improved from 23% to 77%.

Test: ./imagedecoder_fuzzer corpus/
exec/s: 40
Bug: 326543079

Change-Id: I2e36e759c6d68700b4c6f27c77a366c8882b208e
3 files changed