[functors] add convenience shortcut typedefs

dune/xt/grid/functors/interfaces.hh

@@ -39,6 +39,9 @@ public:
   using GridViewType = GL;
   using ElementType = extract_entity_t<GridViewType>;
 
+  using GV = GridViewType;
+  using E = ElementType;
+
   ElementFunctor() = default;
   virtual ~ElementFunctor() = default;
 
@@ -74,6 +77,10 @@ public:
   using ElementType = extract_entity_t<GridViewType>;
   using IntersectionType = extract_intersection_t<GridViewType>;
 
+  using GV = GridViewType;
+  using E = ElementType;
+  using I = IntersectionType;
+
   IntersectionFunctor() = default;
   virtual ~IntersectionFunctor() = default;
 
@@ -115,6 +122,10 @@ public:
   using ElementType = extract_entity_t<GridViewType>;
   using IntersectionType = extract_intersection_t<GridViewType>;
 
+  using GV = GridViewType;
+  using E = ElementType;
+  using I = IntersectionType;
+
   ElementAndIntersectionFunctor() = default;
   virtual ~ElementAndIntersectionFunctor() = default;