QOpenGLWidget and QOpenGLWindow replacement story

Not for Qt 6.0.

What is the story for QOpenGLWidget and friends? Is there a replacement, such as a QRhiWidget or QRhiWindow? Not much sense if QRhi is not public. However, a "QExternalRenderWidget" or something that allows doing custom Vulkan/Metal/D3D/OpenGL but only functional when running with the matching QRhi backend could make sense.

Also ties in to the problem of render-to-texture widgets (QOpenGLWidget, QQuickWidget) that currently rely on OpenGL-based compositing in the backingstore.