Internally, these can be very useful for assembling code fragments.
Externally, our users shouldn't have any SkSL::Statement or
SkSL::Expression objects to pass in, so it's still effectively a non-
public API.
Change-Id: I03b88507ce932b472ab5b9aed68ea67dcd10b13f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/449855
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
b43596f10b