[lldb] [llgs] Convert m_debugged_processes into a map of structs

Convert the m_debugged_processes map from NativeProcessProtocol pointers
to structs, and combine the additional set(s) holding the additional
process properties into a flag field inside this struct.  This is
desirable since there are more properties to come and having a single
structure with all information should be cleaner and more efficient than
using multiple sets for that.

Suggested by Pavel Labath in D128893.

Differential Revision: https://reviews.llvm.org/D129652