Feature request: export_all_to_string function

[Blechlawine]

export_to_string already does this, but only for one single type. export_all_to_string would basically do the same as export_all except output them as a String (Could also be a Vec<String>) to manually create the files for the types.

Currently, one can achieve the same result by manually calling export_to_string() on all types, manually searching for their dependencies, and calling export_to_string() on them as well.