[llvm] [clang-tools-extra] [MLGO] Upstream the corpus extraction tooling (PR #72319)

[Mircea Trofin via cfe-commits]

================
@@ -0,0 +1,6 @@
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
----------------
mtrofin wrote:

why do we need `mlgo/mlgo` - could we just do `mlgo/corpus` and `mlgo/tests/corpus` - this leaves it open to add later non-corpus related things if needed.

Shouldn't the tests go under `llvm/test/tools` like the other utils? There should be a way to disable them if python version is under 3.8.

Also the `lit.local.cfg` should probably go through the dependency list of the package and skip the tests if the packages aren't available. I assume we can do that off `pyproject.toml`

https://github.com/llvm/llvm-project/pull/72319