(feat) (svelte2tsx) Type check event forward from element on component

[jasonlyu123]

Aims to be able to type-check events bubbled/forwarded from an element. https://svelte.dev/docs#on_element_event
Part of #304

Component.svelte

<button on:click></button>

Component2.svelte

<scirpt>
import Component2 from './Component2.svelte
</script>

<Component2 on:click={e => console.log(e)} /> <!--- type check here -->

• Component event type check spec
• Definition of element event forward in the component class
• New Component event type check method
• Component forward event again

[jasonlyu123]

Can't get it to extract event type from $on method, Seems like we might still need to add a def property like $$props_def and $$slot_def

[dummdidumm]

Nice work! There is one problem that remains: When the user defines a custom event, it will not get picked up and it will throw a false type error:

<script>
  import { createEventDispatcher } from 'svelte';

  const dispatch = createEventDispatcher();
  dispatch('hello', 3);
</script>

<script>
  import Child from './Child.svelte';
</script>

<Child on:hello={e => e} /> // <--- throws an error

We somehow need to fall back to the generic Event interface in this case.

[dummdidumm]

Awesome!