Blender Git Loki

Cleanup: Remove spline add_point method, refactor mesh to curve node

It's better to calculate the size of a spline before creating it, and this
should simplify refactoring to a data structure that stores all point
attribute contiguously (see T94193). The mesh to curve conversion is
simplified slightly now, it creates the curve output after gathering all
of the result vertex indices. This should be more efficient too, since
it only grows an index vector for each spline, not a whole spline.