Mention iteration depth for some Iterable methods

Closes #7797

Most of the other suggestions have already been added, add an explicit
mention of shorcutting for `contains`, `firstWhere`, and `single`,

R=lrn@google.com

Change-Id: I53c254839f198a368fcb8734c3f7983b9b3ccad4
CoreLibraryReviewExempt: Doc changes only.
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/310767
Reviewed-by: Lasse Nielsen <lrn@google.com>
Commit-Queue: Nate Bosch <nbosch@google.com>

https://dart.googlesource.com/sdk/+/18374352738e0e845b9725a57820a7b1ade1df6d
1 file changed
tree: dc4d74e5e41abe9718ebef784fbd8eef8b82ffa0
  1. commits.json