Break SkSLInliner mangling out into a separate class

Change-Id: If0300761153d37b026fdc7756018c239ea6ca7ee
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/352505
Auto-Submit: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
5 files changed