[!302] [cmake] Allow wrapping a statistic profiler around the code generation tool chain

Merge branch 'feature/statistic-profiling' into 'master'

ref:extensions/dune-codegen Enable with the cmake variable
DUNE_CODEGEN_PROFILING. For each generated header, a profile is written out.
These can be visualized with tools like snakeviz.

This is the main technical part of [#74], the actual profiling is missing\...

See merge request [extensions/dune-codegen!302]

  [#74]: gitlab.dune-project.org/NoneNone/issues/74
  [extensions/dune-codegen!302]: gitlab.dune-project.org/extensions/dune-codegen/merge_requests/302