C++ updates and code cleanup

[greg7mdp]

• implement proper queue for notifying the main thread
• proper classes for luigi widgets
• update LoadFile to UICode::load() and use it in luigi_example.cpp
• luigi: make UIElement a proper base class of widgets.
• luigi: make the MessageProc member functions
• luigi: remove unneeded UIElement:: and other namespace prefixes
• luigi: remove free functions, create UI class
• luigi: implement UIPainter proper class with member functions
• luigi: replace free UI*Create functions with static class members Create.
• luigi: move X11 and Win32 free functions into classes
• don't use raw pointers unless they are non-owning
• cleanup msgReceivedData / msgReceivedLog / msgReceivedControl
• create breakpoints & BreakpointMgr classes?
• create Debugger class instead of calling stuff like evaluate("gdbf_valueof") or EvaluateExpression(e), which should include the current EvaluateExpression, EvaluateCommand, DebuggerSend, DebuggerStartThread, ...
• Debugger class could also hold the info about the program being debugged, instead of some of it being in SourceWindow like _auto_print_expression, ... (update #ifdef'ed out code too)
• replace remaining char arrays in gf.cpp
• have DisplaySetPosition take a std::string_view and int, and use re to extract the path and line # so we don't copy the string (look for _location)
• use UIPoint instead of x and y
• use clang-tidy gf.cpp --checks=-*,bugprone*,modernize* --fix -- --std=c++23