Adding fuzzers for libstagefright.

This is a first batch of fuzzers written for libstagefright covering the following classes: MediaClock, MediaMuxer, SkipCutBuffer, StagefrightMediaScanner.
Test: These were all ran on a Pixel3a device for at least 48 hours to ensure that the fuzzers were stable.

Signed-off-by: Corbin Souffrant <corbin.souffrant@leviathansecurity.com>
Change-Id: I4e559bb57ee76a530fd01d7e3790133c3fb40349