Added DSL FP codeAppend function.

This also adds the relevant Start() / End() calls so that the DSL
is put into the correct state.

Change-Id: I844b0ab5dff06e3f7b0a69458bf4442a5da0f33e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/364857
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
5 files changed