Use NonRandomizedStringEqualityComparer in HashSet

[danmoseley]

This has been pointed out a few times most recently by @GrabYourPitchforks #1989 (comment)

It adds a bit of complexity, but HashSet<string> is common.

Note we would want the #36252 goodness as well.

Tagging subscribers to this area: @eiriktsarpalis
Notify danmosemsft if you want to be subscribed.