Document and validate typical_p in generation
# What does this PR do?

Throws a `ValueError` when `typical_p` argument is provided to text-generation, but its value or `do_sample=False` prevent typical decoding from happening as intended. Adds a line documenting typical decoding.

Most arguments to generate were previously covered in #18261 , but not `typical_p`.

_The documentation is not available anymore as the PR was closed or merged._