[next 🍒] Parameterize Initialization of 'clang::CodeGenerator' on a TargetInfo instance which may differ from the one in the ASTContext

[artemcm]

As per https://github.com/apple/swift/pull/65930, Swift compiler's built-in Clang instance may require to perform type-checking against one OS version and compilation/code-generation against an earlier version. This change allows Swift to configure it's built-in Clang code-generator with a custom 'TargetInfo'.

Part of rdar://113712186

[artemcm]

@swift-ci test

[bnbarham]

Swift build will fail, you can run llvm tests to ensure it (llvm) builds, but otherwise I'd just merge (@swift-ci please test llvm)