SkZip - synchronized indexing of several pointers

This is the mechanism for syncing a bunch of things with
contiguous memory like vector<>, array<> and SkSpan<>.

In a following CL, a convenience function SkMakeZip will
easily convert most containers into a zip.

Change-Id: Icda5b1774ae21c4c163a663f6d2b0f119f63ccba
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/240200
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
4 files changed