Add a decrated.hh file in the deprecated subdirectory and mark it deprecated

Summary

Since macros cannot so easily be visually deprecated, a fallback implementation is added to allow a quick fix in downstream modules that simply can include the deprecated/deprecated.hh file.

Note, the fallback file does not include CMake checks whether the __attribute__((deprecated)) is available. This would involve another fallback implementation in CMake.

I have put the deprecated file in a subdirectory to not pollute the main common directory with files that are actually already removed. It also highlights in the filename, that the included files are deprecated. This directory can be used in the future for similar fallback implementations. The fallback code will not be included in any other dune-common file and is just for use in downstream modules that cannot or have not yet fixed their code.