[5.9] [Macros] Diagnose top-level expansion of undefined freestanding macro

[rxwei]

Cherry-pick of #65429

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• Explanation: Expanding an undefined macro succeeds silently and causes its arguments to not be type-checked. This is a bad state where incorrect freestanding macro expansion code would slip by and compile to nothing.
• Scope of Issue: Macro resolution where there is a shortcut only meant to apply to custom attributes.
• Risk: No risk to custom attributes, or to defined freestanding macro expanisons. All undefined freestanding macro expansions now go through the constraint system, which is an existing code path that those parsed as MacroExpansionExpr already go through, so the risk should be minimal.
• Testing: Added additional diagnostics tests for top-level freestanding macro expansions in library mode.

rdar://108280416

[rxwei]

@swift-ci please test

[rxwei]

@swift-ci please test macos