Unrestricted OverloadedLabels (#11671)

Resolves this issue: #11671 (closed)

Implements this accepted GHC proposal: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0170-unrestricted-overloadedlabels.rst

I am a first time contributor to GHC. I've done my best to read the wiki and follow the expected MR steps. But it's likely I've overlooked something. Let me know what I can do to fix anything out of place.