green: Fix missing Send bounds on procedures

These were mistakenly not updated as part of the removal of the Send bound by
default on procedures.

cc #13629
Just some general cleanup in the HashMap module

I went through the HashMap module, fixed spelling mistakes, minor
inefficiencies, added tests, and other trivial changes.
auto merge of #13630 : alexcrichton/rust/correct-green-bounds, r=brson

These were mistakenly not updated as part of the removal of the Send bound by
default on procedures.

cc #13629
auto merge of #13646 : cgaebel/rust/hashmap-cleanup, r=alexcrichton

I went through the HashMap module, fixed spelling mistakes, minor inefficiencies, added tests, and other trivial changes. Hopefully this won't be a controversial PR.