Add trailing comma support in cases missing from Swift 6.1

[calda]

Corresponding compiler PR: swiftlang/swift#81612

---

In Swift 6.1, there are many cases where trailing commas should be supported but currently are not:

• 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

This includes cases like:

let foo: (
  bar: String,
  quux: String, // unexpectedly not supported in Swift 6.1
)

let closure: (
  String,
  String, // unexpectedly not supported in Swift 6.1
) -> (
  bar: String,
  quux: String, // unexpectedly not supported in Swift 6.1
)

let foo: Foo<
  String,
  Int,
  Boo, // unexpectedly not supported in Swift 6.1
>

typealias Bar<
  T1,
  T2
> = Foo<
  T1,
  T2,
  Bool, // unexpectedly not supported in Swift 6.1
>

protocol Baaz<
  T1,
  T2, // unexpectedly not supported in Swift 6.1
> {
  associatedtype T1
  associatedtype T2
}

[rintaro]

@swift-ci Please test

[calda]

Failure in the Swift Test macOS Platform job looks unrelated to me -- the Linux test passed 👍🏻

[rintaro]

swiftlang/swift#81612
@swift-ci Please test