WebGL2: Add BlitFramebuffer, ShaderDerivativeSupport

fix from paraboul@

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Debian9-EMCC-GCE-GPU-AVX2-wasm-Release-All-CanvasKit,Test-Debian9-EMCC-GCE-CPU-AVX2-wasm-Release-All-CanvasKit

Bug: skia:9052
Change-Id: If0c408f33f4bb6cd47513a2c1f3a1e3ac3da3320
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249228
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
4 files changed