Move function intrinsic handling into Finalizer

This continues the process of moving code out of IRGenerator and into
better homes.

Change-Id: I4803d39ecb2f4c0e916e82e907b5dcaa285a35ce
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/456116
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
5 files changed