Light-weight C++ API for Qt Quick Shapes and Qt Quick Text

There are multiple use cases where we would like to have arbitrary hardware-accelerated shapes and text in a Qt Quick scene without going through QML or re-inventing existing functionality with custom solutions. Users would also probably want to be able to do this, to easily invent their own graphs representations in a data-driven manner which does not involve passing data from C++ and instantiating Qt Quick items which are easily too expensive when showing tens of thousands of items.

Basically, the only thing we have for users right now is making a QQuickPaintedItem and drawing stuff through QPainter, which quickly becomes too slow when the item grows big because it requires rendering everything in software and then copying the image to the GPU every frame.

Examples where this could be useful internally:

1. Qt Charts 2D
2. Qt Location
3. Rounded rectangles
4. Text renderer which uses Qt Quick Shapes for efficiently handling of large font sizes
5. Canvas API?

Text already has a private API which can be used, but in order for users to benefit from that we should finally take the step and publish it.

For Qt Quick Shapes we should expose the building stones and some data structures, as an internal API first and then when it has been validated we can publish it and users can create custom things like rendering large data sets from sensors which change every frame.