Efficiency improvements in OggExtractor

change from reading 4-bytes at a time to reading 2048-bytes at a time.
Rework backward search so that it no longer repeatedly scans the rest of
the data source as it searches further back; make the backwards scan a
true backwards scan

Bug: 263074833
Test: OggExtractor tests,
Test: playback of problematic ringtone
Merged-In: Ibec81305ca3cae37a990b7d223a10bb8d7864051
Change-Id: I828906d95d14f0ad612bafe6b19494dbd3a037df