WIP: Add support for subpixel font antialiasing to ngl renderer
This pull request adds support for subpixel font antialiasing to the ngl renderer. For GLES Systems, this feature is disabled since I am unsure about hardware support for the required OpenGL extensions. Tagged as WIP due to uncertainty regarding the performance impact of using dual source blending on non GLES-Systems.
Using this patch, gtk4-demo renders as follows:
- With font antialiasing set to greyscale
- With font antialiasing set to subpixel (rgb)