[hybrid] Allow dune-istl MultiBlock types as ranges in forEach

Timo Kochrequested to merge
feature/hybrid-allow-istl-multiblocktypes-as-ranges into master

Currently MultiTypeBlockMatrix can be used as a range in forEach

using namespace Dune::Hybrid;
forEach(m, [](auto& row){
   ...
});

because it has a static constexpr member function size. However, size is deprecated in favour of N. This MR attempt at removing the deprecation warning (because N is looked for first) and also allow types that use a static constexpr member function N to be interpreted as range in the sense of Hybrid::forEach.

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