[Macro] Precise macro plugin dependency during scanning

[cachemeifyoucan]

Teach dependency scanner to track precise dependencies for macro plugin:

• Read the available public external macro module name from swift modules dependencies
• Resolve the macro plugin in the dependency scanner using the search path option
• Pass resolved plugin configuration to swift-frontend so no searching is needed during compilation

This also means if a macro plugin search path is not used, it will not cause an additional module variants due to the search path difference.

rdar://136682810

[cachemeifyoucan]

@swift-ci please smoke test

[cachemeifyoucan]

Please test with following PR: https://github.com/swiftlang/llvm-project/pull/9345

@swift-ci please smoke test

[cachemeifyoucan]

Please test with following PR: https://github.com/swiftlang/llvm-project/pull/9345

@swift-ci please smoke test