Low pre-rendered Version of PdfPage

[LukasKompatscher]

Use case

When scrolling through the pages on a slow device, the white loading screen makes the pdf viewer seem kind of slow. A prerendered but very low quality version of page already rendered would make it seem a lot more fast and also a lot better instead of the white page or even the loading indicator.

Proposal

When going thorough the pages with snapping, and reaching the next page, instead of a loading indicator there should be a low quality version rendered page, which then transforms into the better rendered version if the page has finished loading. This ensures better flow and better UI.