Move _create_event_chain to EventChain.create

[masenf]

The ability to convert EventType arguments into EventChain is crucial for wrapping JS libraries that need to pass event handlers via hooks or other non-component centric interfaces.

Improve typing such that wrapped components accepting EventType arguments can be directly converted to EventChain / EventChainVar to be rendered as JS code.

---

import reflex as rx
from reflex.event import BASE_STATE


class GoogleAuthState(rx.State):
    def on_success(self, data: dict):
        print(data)


def _on_success_signature(data: rx.Var[dict]) -> tuple[rx.Var[dict]]:
    return (data,)


def handle_google_login(
    on_success: EventType[[dict], BASE_STATE] = GoogleAuthState.on_success,
) -> rx.Var[rx.EventChain]:
    on_success_event_chain = rx.Var.create(
        rx.EventChain.create(
            value=on_success,
            args_spec=_on_success_signature,
            key="on_success",
        )
    )
    return rx.Var(
        "() => login()",
        _var_type=rx.EventChain,
        _var_data=rx.vars.VarData(
            hooks={
                """
const login = useGoogleLogin({
  onSuccess: %s,
  flow: 'auth-code',
});"""
                % on_success_event_chain: None,
            },
            imports={"@react-oauth/google": "useGoogleLogin"},
        ).merge(on_success_event_chain._get_all_var_data()),
    )