[infra] Split out gen_tasks logic into its own shareable package

This makes dependent repos (eg. lottie-ci) significantly less hacky.

Bug: skia:9259
Change-Id: I8a933a927608d96e59a017dd7ef8e52d1d828a4d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/227438
Commit-Queue: Eric Boren <borenet@google.com>
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
3 files changed