Particles: Use list of lines for multi-line string serialization

Change-Id: Ic81b3433b485ca9ce0e60bd10ec12706e673ee89
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/229917
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
9 files changed