Is your feature request related to a problem? Please describe.

Code that is stuck with Python 3.8 and cannot use future annotations and has to use List, Optional, Union, etc.

Describe the solution you'd like

It would be nice if it was possible to "modernize" Griffe expressions on-the-fly, transforming Optional[...] into ... | None, Union[A, B] into A | B, etc.

Describe alternatives you've considered

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Additional context

Originally asked by @tiangolo in fastapi/fastapi#10392 (comment)