Use Skia API to detect if FP16 render buffer is supported

Use Skia GrCaps to detect if we can render into a FP16 buffer.
Exclude Extension class initialization from SkiaGL pipeline.

Bug: 68383159
Test: Passed testWindowProducerCopyToRGBA16F on gce_x86_phone emu
Change-Id: I3355bad891ed5403fbd94d18bb8ba110a3b77325