gradients on fonts don't render correctly in FemtoVG renderer

[NigelBreslaw]

See here

The font should look like

[ogoffart]

This is a problem with the femtovg renderer
Looks like the gradient is applied wrongly

This is how it renders with different renderer in master:

The software renderer is also wrong as it doesn't support gradient on anything but plain rectangle background (without border or radius), but that's a known limitation.