Implement Stage 3 Proposal Array.prototype.groupBy

[MadProbe]

Proposal https://github.com/tc39/proposal-array-grouping has reached stage 3 as of TC 39 meeting at December 2021.

Also i want to implement this proposal.

[ppenzin]

@rhuanjl what do you think?

[rhuanjl]

Sounds good to me - looks like it would be easiest to implement as self-hosted javascript in this file: https://github.com/chakra-core/ChakraCore/blob/master/lib/Runtime/Library/InJavascript/Array_prototype.js