[llvm] [docs][CMake] Add CMakePreset, improve VS documentation (PR #84760)

[Tobias Hieta via llvm-commits]

tru wrote:

> Should we explicitly say this isn't for VS Code? I know more people are developing llvm with it now, but I don't think we currently have our docs for it (although there are redhat/linaro blogs on the subject) - I just worry beginners might get confused.

I want to document VSCode next!

https://github.com/llvm/llvm-project/pull/84760