This makes changes to the opensubdiv module to support additional vertex data
besides the vertex position, that is smootly interpolated the same way. This is
different than varying data which is interpolated linearly.
Fixes T96596: wrong generated texture coordinates with GPU subdivision. In that
bug lazy subdivision would not interpolate orcos.
Later on, this implementation can also be used to remove the modifier stack
mechanism where modifiers are evaluated a second time for orcos, which is messy
and inefficient. But that's a more risky change, this is just the part to fix
the bug in 3.2.
Differential Revision: https://developer.blender.org/D14973
All parts of drawing (shaders, GL mesh descriptor, material partitioner
and so on) needs to be redone for the draw manager and new OpenSubdiv
library.
Removing untested code which is doomed to be replaced to make localized
refactoring easier.
C-API is way smaller than the rest of the code which uses it.
So better to conditionally compile stub implementation than
to keep adding ifdef everywhere.
