Make Graphite-Dawn compile against emsdk.

Add bot that compiles canvaskit with Graphite/WebGPU

Bug: b/304842636
Change-Id: I8f7df6b88627b77b6bf52b16c6d852c0fdb71dc4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/770599
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <briansalomon@gmail.com>
12 files changed