[SR-15059] JSON5 support missing from open-source Swift

[swift-ci]

Previous ID	SR-15059
Radar	rdar://problem/81871548
Original Reporter	ryanw (JIRA User)
Type	Bug

Environment

Swift 5.5-dev, FC34

Additional Detail from JIRA

Votes	1
Component/s	Foundation
Labels	Bug
Assignee	None
Priority	Medium

md5: 3417224c6821cdb0321376f444c23656

Issue Description:

I see JSON5 support has been added as an opt-in option to JSONDecoder for iOS 15/macOS 12, however this does not yet seem to have been implemented in the open-source stdlib.

https://developer.apple.com/documentation/foundation/jsondecoder/3766916-allowsjson5

[typesanitizer]

cc @millenomi

@swift-ci create

[mickeyl]

I‘d love to see this. Either in Foundation (preferred) or perhaps in https://github.com/swift-extras/swift-extras-json

[parkera]

This is implemented in swift-foundation's JSONDecoder. See also #5001