Allow for preload progress bar to be a looping animation to handle cases with large files.

[spencerking]

Currently, the preload progress bar updates only when a file is completely loaded. If only a single, large file is being loaded users are left staring at a static bar with no indication anything is happening. I think it's worth exploring estimating how much of each file has been downloaded based on network speed.

If that proves to be non-viable adding in some "Now Loading" text or a loading gif would be better than nothing.

Helpful links:
https://developer.mozilla.org/en-US/docs/Web/API/NetworkInformation/downlink

Edit:
I can't assign this to myself but I will look into this over the next week or so.

[jodeleeuw]

Bumping this to 6.2. It looks like downlink isn't widely supported or stable. The best solution is probably to enable some customization of the progress bar so that it can display a circular loading animation if desired.