[clang-tools-extra] [clangd] [Modules] Support Reusable Modules Builder (PR #106683)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

I'd like to land this in 2 weeks if no more comments came in. Given:
- In our downstream, we've landed this patch for more than a year and it seems running well. And also in the open source world, I tried to send it to https://github.com/ChuanqiXu9/clangd-for-modules . Everyone experienced it didn't complain about it for bugs. So I believe this is well tested.
- There are other following patches and I really wish we can have something workable in the next release.
- This patch doesn't change the shape of modules support in clangd. The major change lives in ModulesBuilder.cpp, which we can think it as an implementation detail instead of some global things.

For policy related comments, please sent it to https://discourse.llvm.org/t/rfc-directions-for-modules-support-in-clangd/78072/6

https://github.com/llvm/llvm-project/pull/106683