Support implicit-dynamic: false in generated code

[DanTup]

If I disable implicit-dynamic I get errors in the generated code. It'd be nice to not have to allow implicit any for just the generated code (I did try adding the generated files to exclude in analysis_options.yaml but that didn't seem to work).

[davidmorgan]

Thanks for reporting. Agreed this is bad -- I think the correct way is to fix for everyone rather than to add an option for it. I'll take a look.

I'm on vacation right now, though, so it will be in a week or so.