New python submodule mathutils.interpolate for various mesh interpolation and weighting methods.

This module will contain mirrored functions for calculating and applying
weights for points on a mesh. This includes barycentric and UV weighting
and possibly more advanced global weighting such as harmonic weights.

The naming should follow this scheme:
<type>_{2d,3d}_{calc,apply}

e.g.
poly_2d_calc
poly_2d_apply
uv_3d_calc
...

Reviewers: campbellbarton

Differential Revision: https://developer.blender.org/D939

source/blender/python/mathutils/mathutils.c

@@ -502,6 +502,7 @@ static struct PyModuleDef M_Mathutils_module_def = {
 
 /* submodules only */
 #include "mathutils_geometry.h"
+#include "mathutils_interpolate.h"
 #ifndef MATH_STANDALONE
 #  include "mathutils_kdtree.h"
 #  include "mathutils_noise.h"
@@ -537,6 +538,7 @@ PyMODINIT_FUNC PyInit_mathutils(void)
 	
 	/* submodule */
 	PyModule_AddObject(mod, "geometry",       (submodule = PyInit_mathutils_geometry()));
+	PyModule_AddObject(mod, "interpolate",    (submodule = PyInit_mathutils_interpolate()));
 	/* XXX, python doesnt do imports with this usefully yet
 	 * 'from mathutils.geometry import PolyFill'
 	 * ...fails without this. */