The GPU evaluation for curves will have to change significantly from the
current particle hair drawing code, due to its more general use cases
and support for more curve types. To simplify that process and avoid
introducing regressions for the rendering of hair particle systems,
this commit splits drawing functions for the curves object and
particle hair.

The changes are just inlining of functions where necessary.

Next steps:

• Remove reuse of EEVEE_HairMotionData and ParticleHairCache structs.
• Move/duplicate necessary code to a separate draw_curves.ccfile.