Generalize KeyframeAnimatorBuilder to AnimatorBuilder

Change-Id: I116489a1261a93d9b2513ca53f04e1305e6fd85b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/432957
Reviewed-by: Florin Malita <fmalita@chromium.org>
Reviewed-by: Avinash Parchuri <aparchur@google.com>
Commit-Queue: Avinash Parchuri <aparchur@google.com>
10 files changed