Infinite scrolling media gallery

[ara4n]

Is your feature request related to a problem? Please describe.

There is no way to view an index of the images/files in a room in EX today.

Meanwhile other apps like WhatsApp, Threema and (to a lesser extent) iMessage provide a really delightful UI of an infinite scrolling gallery per room, so you can rapidly flip through all the old images etc and find what you're after - effectively using the room as a scrapbook.

Describe the solution you'd like

Infinite scrolling grid of media (and also the ability to swipe left & right between media when viewing a specific instance).

Content should be pulled from the local cache if present; if not, paginated serverside using filtered APIs - not using the slow "paginate everything and check whether it's an image or not" that the legacy apps did... apart from in E2EE rooms, where we already have to spider all content anyway to check for keyword mentions.

Describe alternatives you've considered

let's not repeat the awful UI of EI

Additional context

this feature is basically table stakes, when comparing with our competition.