[pathkit] Add .ready() to initialize

See https://github.com/kripken/emscripten/issues/5820 and
https://skia-review.googlesource.com/c/skia/+/181177 for more context.

(Problem was discovered in CanvasKit, and this ports the same fix to
PathKit).

Bug: skia:
Change-Id: Ic8b2fb399210631a571595a5b3d11d1736c00def
Reviewed-on: https://skia-review.googlesource.com/c/181178
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
15 files changed