[lldb/Bindings] Move bindings into their own subdirectory

All the code required to generate the language bindings for Python and
Lua lives under scripts, even though the majority of this code aren't
scripts at all, and surrounded by scripts that are totally unrelated.

I've reorganized these files and moved everything related to the
language bindings into a new top-level directory named bindings. This
makes the corresponding files self contained and much more discoverable.

Differential revision: https://reviews.llvm.org/D72437