[lldb/Plugins] Add ScriptedProcess Process Plugin

This patch introduces Scripted Processes to lldb.

The goal, here, is to be able to attach in the debugger to fake processes
that are backed by script files (in Python, Lua, Swift, etc ...) and
inspect them statically.

Scripted Processes can be used in cooperative multithreading environments
like the XNU Kernel or other real-time operating systems, but it can
also help us improve the debugger testing infrastructure by writting
synthetic tests that simulates hard-to-reproduce process/thread states.

Although ScriptedProcess is not feature-complete at the moment, it has
basic execution capabilities and will improve in the following patches.

rdar://65508855

Differential Revision: https://reviews.llvm.org/D95713



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>