Previously we expanded out all the program variations into individual enums
but as we add more variations this becomes hard to maintain. Generate the
BlitGL program based on the individual parameter instead.

BUG=990368

Change-Id: I94fd5132baa5b6828aec7823ca5d9f0ffe94379f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1834581Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>