fix: CodeGen correctly produces yyyy-mm-dd format for date with examples

[Zemke]

When an example was specified for a property with the date format, its example would be generated to something like Sat Jan 30 01:00:00 CET 2021.

It's because the resolved type for a date example is a DateSchema which uses java.util.Date to represents the date causing toString() to not conform to the yyyy-mm-dd format.

This is somewhat analogous to example generation in #17495.

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[wing328]

Thanks for the PR but your commit (as shown in the Commits tab) is not linked to your Github account, which means this PR won't count as your contribution in https://github.com/OpenAPITools/openapi-generator/graphs/contributors.

Let me know if you need help fixing it.

Ref: https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-can-i-update-commits-that-are-not-linked-to-my-github-account

[Xiphoseer]

As far as I can tell, this should fix #15342?

[Zemke]

Yes.