Introduce SkIota a wrapper that adds an index

SkIota adds an index to some collection you already use:

std::vector<int> v;
for (auto t : SkMakeIota(v)) {
   size_t i; int v;
   std::tie(i, v) = t;
   ...
}

Change-Id: I18390fc084eb8509cfaeb50d9720541759a2986d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/225546
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
5 files changed