Error when reference is passed to component without $

[crcn]

This should error:

<div export component as="Component" {class?}>
</div>

<!-- This should show a warning -->
<Component class="test">
</Component>

[crcn]

This requires #845 in order to work because of this scenario:

<div component as="Component" class={customClassName?}>
</div>

<!-- this needs to error -->
<Component customClassName="boom" />