3 component texture formats are often not supported by vulkan devices.
Sometimes the support is less than 5%. The 4 components variants have
more than 90% support.
This PR builds on top of the existing vulkan data conversion to add
the ability to convert between RGB16F<=>RGBA16F and RGB32F<=>RGBA32F
texture formats.
This allows using color management other then Standard/sRGB. Most places
the 3 component texture formats are phased out, but OCIO, external
render engines and real time compositor uses them.
Jeroen Bakker