[lldb/Lua] Add Boilerplate for a Lua Script Interpreter

This adds the boilerplate necessary to support the Lua script
interpreter. The interpreter is not functional yet and just reports that
it's not implemented.

Discussion on the mailing list:
http://lists.llvm.org/pipermail/lldb-dev/2019-December/015812.html

Differential revision: https://reviews.llvm.org/D71232