Curves: Add surface UV map name property

In the latest discussions about curves/hair mesh attachement
information (T95776), it was decided to use UV coordinates to
store where on the mesh each root is. For that, we have to specify
which of the UV map attributes to use for UV lookups.

This property isn't used yet, but it will be shortly when refactoring
the attachement information in the add brush and the to particle
system conversion.

Differential Revision: https://developer.blender.org/D15115

source/blender/makesrna/intern/rna_curves.c

@@ -292,6 +292,14 @@ static void rna_def_curves(BlenderRNA *brna)
   RNA_def_property_ui_text(prop, "Surface", "Mesh object that the curves can be attached to");
   RNA_def_property_update(prop, NC_OBJECT | ND_DRAW, NULL);
 
+  prop = RNA_def_property(srna, "surface_uv_map", PROP_STRING, PROP_NONE);
+  RNA_def_property_string_sdna(prop, NULL, "surface_uv_map");
+  RNA_def_property_ui_text(prop,
+                           "Surface UV Map",
+                           "The name of the attribute on the surface mesh used to define the "
+                           "attachment of each curve");
+  RNA_def_property_update(prop, 0, "rna_Curves_update_draw");
+
   /* Symmetry. */
   prop = RNA_def_property(srna, "use_mirror_x", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, NULL, "symmetry", CURVES_SYMMETRY_X);