[Roadmap 2025] shiboken6: Better handling of non-default constructible or other special value types

Non-default constructible <value-type> (like recently added QWebEngineFrame QWebEngineDesktopMediaRequest ) cause some issues with shiboken since the copy conversion used for function arguments requires a default constructor.

Using <object-type> is not always an alternative since then, function return by value does not work and crashes occur when emitting signals passing by const-ref.

In the future, there might also be other special cases like move-only types.

• Better detection of constructibility from clang
• Added attributes for overriding code model detection of constructibility
• Fixed crash when passing types with pointer conversion only by const ref in Qt Signals
• Handle Move only types
• Fix passing non-default constructible types by ref
• Streamlined code