[lldb] Introduce OperatingSystem{,Python}Interface and make use it

This patch aims to consolidate the OperatingSystem scripting affordance
by introducing a stable interface that conforms to the
Scripted{,Python}Interface.

This unify the way we call into python methods from lldb while
also improving its capabilities by allowing us to pass lldb_private
objects are arguments.

Differential Revision: https://reviews.llvm.org/D159314



Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>