[TypeIndex] Make GlobalGeometryTypeIndex::base() public

It's a useful method (and required by PDELab), so make it publicly
available.

(cherry picked from commit c7cd5780feb3bcad8f0c9b45adbb6561f85b20ad)
Signed-off-by: Steffen Müthing <muething@dune-project.org>

dune/geometry/typeindex.hh

@@ -114,6 +114,7 @@ namespace Dune
       return (1 << dim) >> 1;
     }
 
+  public:
     /**
      * \brief Compute the starting index for a given dimension including
      *        irregular geometry types
@@ -124,7 +125,6 @@ namespace Dune
       return regular_base(dim) + dim;
     }
 
-  public:
     /**
      * \brief Compute total number of geometry types up to and including the
      *        given dimension