[recipes] Add asset_version utility function.

Bug: skia:7720
Change-Id: I044ca5281354b21c9deffa408ad7ec20c51d2e2e
Reviewed-on: https://skia-review.googlesource.com/115122
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Ben Wagner <benjaminwagner@google.com>
142 files changed