Convert the current selection to aTArray, optionally converting to ConvertToType. For (Tri|Group)=>Vtx, all triangle vertices (in triangles or PolyGroups) are included. For Vtx=>Tri, all one-ring vertices are included. For Group=>Tri, all Triangles are found via enumerating over mesh. (Tri|Vtx)=>Group, all GroupIDs of all triangles/one-ring triangles are included