Add support for pointer events to pc-entity

[willeastcott]

Add support for the following pointer events to the pc-entity element:

• pointerdown
• pointerup
• pointermove
• pointerenter
• pointerleave

You can do:

<pc-entity onpointerdown="console.log('clicked!')"></pc-entity>

Or:

const entity = document.getElementById('my-entity');
entity.addEventListener('pointerdown', (e) => {
    console.log('clicked!');
});

[marklundin]

It would be awesome to also have event bubbling here and set the event handle on parent entities

[willeastcott]

It would be awesome to also have event bubbling here and set the event handle on parent entities

Agreed. I'll do that in a follow up PR.