This change adds ExternalTextureManager which implements
InputListener to only queue input frames to the
ExternalTextureProcessor when it is ready to accept an input
frame. This replaces the old retry-logic in GlEffectsFrameProcessor.
Before this change, the retrying in GlEffectFrameProcessor wasted
CPU time if input becomes available faster than the
ExternalTextureProcessor can process it.
PiperOrigin-RevId: 467177659
