[clang] [clang][Tooling] Insert global module fragment during header insertion (PR #173724)

[Sirui Mu via cfe-commits]

Lancern wrote:

@ChuanqiXu9 I Opened an issue in `clangd/clangd` to track this: https://github.com/clangd/clangd/issues/2577

https://github.com/llvm/llvm-project/pull/173724