Add Support for Asset Streaming

[rayanmargham]

What problem does this solve or what need does it fill?

Currently bevy loads images all into ram, this is fine for projects that don't use huge image sizes but for projects that load huge images (4k-8k textures) this isn't viable as ram usage can go up to 300mb PER image.

What solution would you like?

Add support for streaming image data live. I'm not sure how'd that look like as I'm not very competent with how bevy works at the backend.

[alice-i-cecile]

So, this is more broadly "asset streaming": we care about this for audio and meshes as well.

Unless we want to pursue a "read directly from disk" strategy, we instead need a just-in-time solution: predicting what assets are about to be needed, starting the asset loading process, and then dropping those handles when they're no longer needed.