Sometimes uniforms get wrong type from QML -> C++ -> GLSL

For example when setting a parameter to a value of 2.0 in QML, we end up with bad data in the float being passed to GLSL. I think this is caused by the 2.0 being represented as an integer within the variant used to get the data to the backend.

The backend knows the uniform is of type float so I think it's a missing int -> float cast somewhere.