[5.3][ModuleInterface] Prefer the swiftmodule in the SDK over the prebuilt-module cache

[xymus]

Fix the search order for module interfaces to respect the documented behavior:

1. Local cache
2. Next to the .swiftinterface
3. Prebuilt cache

Fixing the order of the last two allows the XcodeDefault compiler to prioritize swiftmodule files with SPI information.

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• Explanation:
  The compiler was picking swiftmodules from the prebuilt-module cache over those next to the swiftinterface files. The prebuilt-modules are public so then don't have SPI information. As such, even when SPI was available to a project the compiler couldn't see it.
• Scope of Issue: Affects an internal project building with the default toolchain while using SPI.
• Origination: Around the introduction of the prebuilt-modules cache, however this issue was made visible by the addition of Swift SPI.
• Risk: Relatively low. The fix respects the intended behavior as it was originally documented. While it affects the module loading order of all projects most projects don't build with both the prebuilt-cache and swiftmodule files next to the swiftinterface files.
• Reviewed By: Xi Ge
• Resolves: rdar://problem/64097455
• Cherry-pick Of: [ModuleInterface] Prefer the swiftmodule in the SDK over the prebuilt-cache #32423

[xymus]

@swift-ci Please test

[xymus]

@swift-ci Please nominate