Duplicating children fix for {shadow: false}

[AtnesNess]

When shadowDOM is not attached and developer wants to render children inside react component it will lead to duplicating of children.

1. Children will be placed at slot as intended
2. Children will remain at the and of the node, because after rendering original content won't be cleared

[rozek]

I just tried the fix shown here and have to admit that it does not work properly: while it indeed deletes one of the two child instances, it removes the first one rather than the second.

As a consequence, componentDidMount will be called for the child instance that will be deleted right afterwards, but never for the instance that "survives". Programs relying on componentDidMount (like mine) will therefore fail...

[rozek]

My solution: instead of modifying the source of "preact-custom-components", I got rid of the duplicated child elements using a "trick" mentioned in issue #32:

for a component with inner elements add a <slot/> tag instead of ${props.children}

This workaround sounds strange, but it works (somehow):

• the <slot/> tag will be rendered as <div><slot></slot></div> and
• the actual child elements will be rendered as direct descendants of the container element, right next to the <div><slot></slot></div>

This may not look nice, but I can live with that hack...