Changes included: 1. Enable MP4 extractor to read all types of metadata. 2. Allow passing String and Float metadata via Transformer. Reference to QuickTime spec: https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/Metadata/Metadata.html#//apple_ref/doc/uid/TP40000939-CH1-SW21 PiperOrigin-RevId: 538783982 (cherry picked from commit 8ce74aa4000d7b6bb9673734c42c3620cd602544)
