Qt 6: Connection syntax migration

To what extent can the old connection syntax be deprecated?

Points to consider

• uic currently generates the old syntax
• uic calls QMetaObject::connectSlotsByName()

Potential action points/TBD

• Port uic to generate Qt 5 syntax. That would require to generate QOverload for any function with parameters, but then QOverload would have to be made agnostic of "const QString &" vs "QString") first.
• Drop QMetaObject::connectSlotsByName() from uic (option?) or
• Change QMetaObject::connectSlotsByName() to output warnings and maybe the connections in C++ so that it can be easily added
• Add a per-form setting to Designer so that connectSlotsByName() can be disabled by form for migration?