include Atdgen_codec_runtime in Atdgen_runtime

[wokalski]

This would be consistent with Atdgen_runtime on native. I stumbled upon this inconsistency when I wanted to use Type_Field adapter in bucklescript. I had to workaround the difference between native and bs by creating a Atdgen_universal_runtime and using it from .atd.

[ygrek]

ref ahrefs/atd#156