Fix two SkPathRef bugs

- Transforming a path in place wasn't updating the gen ID of the path
- Transforming a path into another (uniquely held) path wasn't calling
  gen ID change listeners.

Bug: skia:
Change-Id: I9e244725d9bd5776d203ce6b12698cee09d0b714
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/199003
Auto-Submit: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Reed <reed@google.com>