TF Coverage Scripts and Tutorial

[Kristoff-starling]

• Sanitize and push TF coverage evaluation scripts.
• Add tutorial in experiments/README.md.

[ganler]

Attaching the TensorFlow thread regarding the Clang build: tensorflow/tensorflow#57872 (comment)

Not sure if it would allow building TensorFlow with LLVM coverage such that we can simply reuse the toolset. The other way around is to use gcov for PyTorch as others -- but the performance is an issue (as gcov is inclined to distribute the coverage information across multiple files making parsing slow)