Typing spec update: PEP 712 `converter` in `dataclasses` Field spec params

[thejcannon]

PR: python/typing#1783
Discussion on PEP 712 (rejected adding to stdlib dataclasses, but community seemed in-favor of dataclass_transform addition).

This already is implemented in Pyright: microsoft/pyright#5034

❤️ Thanks y'all!

TC sign-off

• Carl
• Eric
• Jelle
• Rebecca
• Shantanu

[erictraut]

@thejcannon, thanks for doing this. Could you please announce this PR in the discourse thread so the community has a chance to review it? We should then wait a week to see if any further comments come in.

[erictraut]

For reference, here's a link to the discourse thread.

[thejcannon]

For reference, here's the Typing council approval in Discourse: https://discuss.python.org/t/discuss-adding-converter-to-dataclass-transform/55125/5