Move Ganesh-specific bits of StrokeTessellator into an #ifdef

Bug: skia:12524
Change-Id: I31ddee40fed6e57caafe7a51fdd90459bd29cd6a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/474356
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
7 files changed