Implement SkTLazy using std::optional

Change-Id: I3d3f175892d23ff5db2c14600c5168273fca8efb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/501840
Reviewed-by: Ben Wagner <bungeman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
2 files changed