Implement the dynamic typed array

[JohanMabille]

This class should provide a std::vector-like API on top of a std:variant<typed_array<all_base_type_t>>. This requires first:

• Implement reference proxies in variable_size_binary_layout #35
• Implement a variant iterator #100
• Implement missing MPL tools for the array class #111
• Implement the null layout for std::nullopt_t #115
• Make the typed array class movable #116
• Implement non-const methods in the array class #123

[JohanMabille]

This implementation is done.