perf: virtual scroll for overview and quick overview

[jakobkordez]

Fixes slow loading and scrolling for large presentations

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[kermanx]

Thanks for your contribution!

There is a problem that the height of the rows is calculated dynamically, but the itemHeight given to useVirtualList is a static value. I am not very sure on this.

[kermanx]

There is a problem that the height of the rows is calculated dynamically, but the itemHeight given to useVirtualList is a static value. I am not very sure on this.

Fixed.

[jakobkordez]

Don't merge yet, fixing something

[jakobkordez]

Ok, that's all

[antfu]

I am not very sure about this - after this PR, every time you open up the overview, every slide gets re-initiated, which they are supposed to be cached.

If perf/memory is really a concern, I'd suggest we take a screenshot of the final slide and place the overview with that image (with an option to opt-in/out) so we don't duplicate slides rendering and would be a lot more performant than virtual scroll.

[jakobkordez]

If you need a large presentation for testing try: https://gitlab.vegova.si/rkv/prosojnice

[jakobkordez]

@antfu Are you sure the slides are not getting cached? It seems to me they are: the loading component only shows the first time the page is opened