Site: Document svelte/easing

[pngwn]

This PR documents svelte/easing and adds an ease visualiser to the examples section.

There doesn't really seem to be a way to add interactive widgets to the Docs without making some changes so, as discussed previously, I've added it to the examples section. I updated the relevant section in the API reference, adding a link to the visualiser and a brief overview of all of the functions exported from that module.

The only significant issue is the fact that the 3-panel display makes the preview window quite small on first load. I've worked around this partly by making the visualiser mobile friendly (ish). It isn't friendly to all device sizes and widths but it seems to work fine on desktop and mobile (portrait).

There are a lot of changes in this PR because I had to update half of the folder names in content/examples to get the easing example in the right slot (I put it just after animations).

Closes #2537.

Edit: Github is rendering my tabs all weird and I don't know why. I'm pretty sure I'm using the same indentation everywhere, I've even quadruple checked. No clue.

[Conduitry]

I think my only complaint right now is that the list of the easings on the API page takes up a lot of vertical space. Is there some nicer way to arrange these into a table? I understand that this is rendered from markdown and the formatting options are limited.

[pngwn]

The table seems better, how do you feel about this:

Edit: Slightly cramped on mobile but not unreadable. I could lose the ease names on the left and it would probably fit more comfortably.

[Conduitry]

👍 Yep definitely better