Tiled Gallery: handle failed uploads gracefully

Impacted plugin

Jetpack

Quick summary

If one tries to upload a disallowed image file type (e.g. .avif), it shows the image preview during "upload", and then the image disappears without any message.

Reported in p8oabR-1wt-p2#comment-8009.

Steps to reproduce

See summary.

A clear and concise description of what you expected to happen.

At minimum there should be some messaging to let the user know that not all the selected images were uploaded. In an ideal world, it'd list which file(s) failed.

What actually happened

See summary.

Impact

Some (< 50%)

Available workarounds?

No but the platform is still usable

Platform (Simple and/or Atomic)

No response

Logs or notes