Support tangent space handedness

[Jhonnyg]

Tangents are now produced as vec4 in the engine, where the fourth component is the handedness of the tangent vector. This can then be used to calculate the correct tangent space vectors in a shader:

vec3 bitangent = cross(normal, tangent.xyz * tangent.w);

Fixes #8733

[matgis]

I think we need to pass on the unaltered W component of the tangent when transforming to world space? 🤔

[matgis]

When using world-space meshes, the tangents in :tangent-data will be transformed by the renderable-data->world-direction-v4 function. Currently, this writes a zero for the W component when it calls the geom/transf-n4 function. I think we need to update geom/transf-n4 to pass along the unaltered W component.

It seems to me, we would need to do something similar on the engine side since we presumably transform the tangents using the normal matrix somewhere there as well, but I'm not seeing it in this PR? 🤔