Refactor some IRGenerator functions

This CL adds additional variants of some IRGenerator functions to enable
them to be more easily called from upcoming DSL code. This should not
change functionality (other than a slightly different error message in
one case).

Change-Id: Ic727c194fca5111d4283007f4ec23653598a853b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/350017
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
Auto-Submit: Ethan Nicholas <ethannicholas@google.com>
2 files changed