[lldb/bindings] Expose the progress reporting machinery to the SWIG interface

This patch defines the SBDebugger::eBroadcastBitProgress enum in the SWIG
interface and exposes the SBDebugger::{GetProgressFromEvent,GetBroadcaster}
methods as well.

This allows to exercise the API from the script interpreter using python.

Differential Revision: https://reviews.llvm.org/D120100



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