Change the order of arguments to GrFragmentProcessor::Compose

This makes the function comment "... composes `f` and `g` into f(g(x))"
true. The alternative would be to just fix the comment (and maybe rename
the arguments), but I find this order of arguments less surprising for
something doing function composition.

Change-Id: I38e2ea81402d829c0850713cc060fe16cb19ae28
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/384319
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
6 files changed