Migrate FunctionCall conversion out of IRGenerator.

We don't currently do FunctionCall optimization, but implementing
something along the lines of skia:10835 would probably involve doing
rewrites for optimization in FunctionCall::Make. This CL is the first
step down that road.

Change-Id: I249b02412e7ebac21bb98d6c5d61af3dcd6f1e69
Bug: skia:11342
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/387156
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
7 files changed