[clang-tools-extra] [clangd] [C++20 Modules] Try to use prebuilt modules (PR #155360)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

Given its simplicity and usefulness, I'd like to land this in late of the next week if no more comments come in.

https://github.com/llvm/llvm-project/pull/155360