Rely less on anchors

[Rich-Harris]

Currently, Svelte peppers the DOM with comments for every {{#if..}} or {{#each...}} block:

<!--#if visible-->

In many cases (e.g. where the block is that last thing in the element's fragment, or where the block is followed by an element that is never removed) that's unnecessary.

[Swatinem]

I was thinking about this a bit. I already factored this out into generator.createAnchor.

The changes needed are a bit complex though.

• The previous sibling needs to know if the next sibling is a static element or not to avoid creating an anchor.
• And the next sibling needs to know that is actually needs to create an identifier (see needsIdentifier of generator.addElement).

I would have to read through your snippet code to understand how it works, maybe it can be leveraged to do something like this.