Qt Quick batch rendering issue when a batch contain nodes that have different index types

When a batch contains nodes that have different index types, there is a rendering issue when the first node of the batch use QSGGeometry::UnsignedShortType: nodes that use QSGGeometry::UnsignedIntType are incorrectly rendered

The attached project defines two custom QQuickItem, a triangle that uses unsigned short indexes and a circle that uses unsigned int indexes.

• When the application is launched, everything is ok: circles are well rendered.
• After pressing the button, the opaque circle is batched with an opaque triangle item (that uses unisgned short indexes) and is incorrectly rendered
• After pressing the button again, the triangle disappears (visible: false) and the two circles are well rendered

Renderer::uploadBatch (qsgbatchrenderer.cpp line 2009) assumes that all QSGGeometryNode nodes use the same index type (QSGGeometry::UnsignedShortType or QSGGeometry::UnsignedIntType) when it computes its canMerge flag

Renderer::prepareOpaqueBatches (qsgbatchrenderer.cpp line 1692) does not check if QSGGeometryNode nodes use the same index type

Steps to reproduce:

1. Please run the attached example
2. Click on the button