Fix of paint on supports don't work for object that has been scaled up #6718

The triangle-ray intersection function used a hard coded epsilon,
which did not work for triangle meshes, that were either too small
or too large. Newly the epsilon may be provided to the AABBTreeIndirect
search functions externally and IndexedMesh calculates a suitable
epsilon on demand from an average triangle mesh edge length.

src/slic3r/GUI/MeshUtils.hpp

@@ -112,7 +112,7 @@ public:
     // The class references extern TriangleMesh, which must stay alive
     // during MeshRaycaster existence.
     MeshRaycaster(const TriangleMesh& mesh)
-        : m_emesh(mesh)
+        : m_emesh(mesh, true) // calculate epsilon for triangle-ray intersection from an average edge length
     {
         m_normals.reserve(mesh.stl.facet_start.size());
         for (const stl_facet& facet : mesh.stl.facet_start)