This is a rework of patch [D10833](https://reviews.llvm.org/D10833)
previously posted on LLVM Phabricator by arthurp in 2015. It allows to
retrieve the type of binary operator via libclangs python bindings.
I did clean up the changes, removed unrelated changes and rebased the
changeset to the latest main branch. As this is my first contribution to
the LLVM project, let me know if any required tests or documentation are
missing.
