[macros] allow forwarding generic arguments through macro declarations

[ktoso]

• Depends on: SwiftSyntax change [macros] prepare generic arguments for replacement in macros swift-syntax#2450
• Unblocks: [Distributed] Add DistributedProtocol macro #71090 distributed actor's #resolve macro.
• Resolves rdar://122004157

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Specifically, this pattern is necessary:

@freestanding(expression) macro checkGenericHashableCodable_root<A: Hashable, B: Codable>() = 
  #externalMacro(module: "MacroDefinition", type: "GenericToVoidMacro")
@freestanding(expression) macro checkGenericHashableCodable<A: Hashable, B: Codable>() = 
  #checkGenericHashableCodable_root<A, B>()

#checkGenericHashableCodable<String, Int>

it seems we never considered this requirement, so this adds the ability to "replace" the A and B inside the "outer" macro's expansion such that the "root" also gets to see String and Int, and not just A and B.

I'll need some help figuring out what can be changed as is in this PR, and what changes we need to stage in - so we don't get compat issues with swift syntax.

[ktoso]

@swift-ci please smoke test

swiftlang/swift-syntax#2450

[ktoso]

swiftlang/swift-syntax#2450

@swift-ci please smoke test

[ktoso]

@swift-ci please smoke test