feat(types): support find definition for jsx tags, events

[johnsoncodehk]

StringKeyOf seem has no practical effect, unused it to support find definition for jsx tags and events in IDE.

[pikax]

LGTM

The type is slightly different but I think there's no real world implications

type StringKeyOf<T> = Extract<keyof T, string>

type EventHandlers<E> = {
  [K in StringKeyOf<E>]?: E[K] extends Function ? E[K] : (payload: E[K]) => void
}

type EventHandlers2<E> = {
  [K in keyof E]?: E[K] extends Function ? E[K] : (payload: E[K]) => void
}

declare const SS: unique symbol
type DDD = EventHandlers<{ [SS]: 1 } & { [number: number]: 'ee' }>
type DDD2 = EventHandlers2<{ [SS]: 1 } & { [number: number]: 'ee' }>

An extra set of eyes might be good here