[6.2] Add trailing comma support in cases missing from Swift 6.1

[calda]

Corresponding compiler PR: swiftlang/swift#81653

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Explanation:

This PR fixes bugs in Swift 6.1 where trailing commas are unexpectedly not allowed.

Scope:

This PR fixes a parsing bugs related to trailing commas in a small handful of places:

• tuple types
• closure types
• generic types
• protocol declaration primary associated type lists

Issues:

• Trailing comma not supported in tuple types or closure types despite SE-0439 swift#81485
• Trailing comma not allowed in generic argument lists despite SE-0439 swift#81474

Original PR:

#3080

Risk:

Low: Targeted parsing change in a few places missed in the original implementation from Swift 6.1

Testing:

New test cases, Swift CI

Reviewers:

@rintaro

[rintaro]

swiftlang/swift#81653
@swift-ci Please test