BlitFramebuffer has issues on some platforms with large source/dest
textures. As per the WebGL2 spec, this was caught with validation for
sizes over 2^32, but there is a specific issue on Linux NVIDIA where it
fails on sizes over 2^16. A better workaround (from chromium), resizes
the blitframebuffer call based on the framebuffer size.

Bug: chromium:830046
Change-Id: Ic6196db6228d0d0ac92b12a68bbced76dcbcdf8c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1707115Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>