Create useExternalFormApi hook

[matthewdavi]

This PR addresses an issue I raised here, #1595.

The new useExternalFormApi hook would make working with forms more ergonomic, as they are already external stores and there are many usecases for reading / writing to a store from outside of the react lifecycle.

[crutchcorn]

This sounds like a terrible way to introduce memory leaks into your app. Can you provide programmatic usage for why we'd want to add this?

[matthewdavi]

This sounds like a terrible way to introduce memory leaks into your app. Can you provide programmatic usage for why we'd want to add this?

Yes actually, i've been chatting on Discord with @LeCarbonator about this and I've created a sample repo. Can I add you to it?

[crutchcorn]

Sure! I'm hesitant, because it sounds a bit like going against React best conventions, but happy to take a look at least.

[matthewdavi]

Sure! I'm hesitant, because it sounds a bit like going against React best conventions, but happy to take a look at least.

I've added you. This seems fairly natural to me since it follows a similar headless pattern as Tanstack Store, and even Tanstack Query, which create their queryClients and stores at module level, which allows for much better ergonomics, being able to read / update values without being tied to the React lifecycle and passing props, or being within a specific context provider.