[clang] [clang][modules] Add single-module-parse-mode callback (PR #179714)

[Qiongsi Wu via cfe-commits]

https://github.com/qiongsiwu approved this pull request.

Thanks for the PR! The API change looks good to me in the context that `moduleLoadSkipped` is to be used in https://github.com/llvm/llvm-project/pull/180047. 



https://github.com/llvm/llvm-project/pull/179714