[clang] [analyzer][docs] Document how to use perf and uftrace to debug performance issues (PR #126520)

[Balazs Benics via cfe-commits]

https://github.com/steakhal commented:

Sorry about the noise of "closed PRs" due to the removal of my repo.
I had difficulties with Github that made me try different solutions to solve that.

In any case, I fixed all the review comments.
Thanks for the excellent recommendations!

https://github.com/llvm/llvm-project/pull/126520