[5.9] always use the argNames constructor for macro DeclNames

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Cherry-pick of https://github.com/apple/swift/pull/66497

• Explanation: Macros with no parameters have an inconsistent DeclName based on whether they were loaded from source code or a built-module.
• Scope: Affects symbol graphs (and Swift-DocC documentation) for these macros.
• Issue: rdar://110179186
• Risk: Low. The deserialization logic that was removed was identical to the one that was left in its place, with the exception of which DeclName constructor is being used.
• Testing: A test has been added to ensure that a parameterless macro has the same name regardless of whether it's loaded from source code or a built module.
• Reviewer: @DougGregor

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@swift-ci Please test

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@swift-ci Please test

[QuietMisdreavus]

@swift-ci Please test