WIP: cxx-qt-gen: use original bridge definition in CXX and remove camel/snake conversion

[ahayzen-kdab]

Closes #616

Closes #532

[ahayzen-kdab]

This works quite well from a generation side, only the qproperty is potentially fun to sort out syntax wise.

However for qproperty we do not pass it straight through and generate methods from it 🤔

The syntax could be something like

#[qproperty(i32, my_property, cxx_name = "myProperty")]
#[qproperty(i32, myProperty, rust_name = "myProperty")]
#[qproperty(i32, my_property, cxx_name = "myProperty", read = Self::custom_read)]

But note that we might have custom getters and setters in there later too 🤔

Another route could be to require to specify the "name" in C++ as the property name and then specify the field it maps to (Name = Self::Field) eg

#[qproperty(i32, myProperty = Self::my_property)]
#[qproperty(i32, myProperty = Self::my_property, read = Self::custom_read)]

Then it could also fallback to if you don't specify the right side it assumes that they are the same

#[qproperty(i32, myProperty)]  // would look for Self::myProperty

Or a further idea could be to make everything key-values, combine the C++ name with the type

#[qproperty(myProperty = i32, member = Self::myProperty)]
#[qproperty(myProperty = i32, read = Self::custom_read)]

Or if we can use the generic syntax

#[qproperty(myProperty<i32>, member = Self::myProperty)]
#[qproperty(myProperty<i32>, read = Self::custom_read)]

Which could also drop the Self

#[qproperty(myProperty<i32>, member = myProperty)]
#[qproperty(myProperty<i32>, read = custom_read)]

[LeonMatthesKDAB]

Hm, I do like the automatic camel-case/snake-case conversion, as snake-case code does look very out of place in QML/C++.
Though that's potentially just me not being used to it.

I believe we could still make the passthrough work with case conversion, by simply checking whether there's a cxx_name or rust_name associated with the qinvokable and if not, injecting only that attribute and leaving the rest alone, which would still be basically a pass-through, with just one additional attribute.

It's something that we should discuss at the company meeting, whether people think camelCase is important in QML.

[LeonMatthesKDAB]

Another suggestion for naming of properties:

    extern "RustQt" {
        #[qobject]
        #[qproperty(
            i32, my_property,
            cxx_name="my_prop",
            setter=set_my_prop)]
        type MyThing = super::MyThingRust;

        #[cxx_name="..."]
        fn set_my_prop(self: Pin<&mut MyThing>, value: i32);
    }

It basically boils down to requiring you to declare the actual setter in the bridge yourself, if you don't want to use the auto-generated one.
That way you have full control.

[ahayzen-kdab]

This has been done via various changes with @BenFordTytherington 's refactorings. Instead of passing through the original we now rebuild in the generation phase this allows for ensuring we have a supported API etc.