[clang-tools-extra] [clangd] [C++20] [Modules] Add scanning cache (PR #125988)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

Update: I asked the Scanner to not run again after global scanned. I felt this was an simple over sight. It doesn't make sense to ask a scanner to scan globally multiple times.

https://github.com/llvm/llvm-project/pull/125988