Improve "Error downloading message" by restyling and adding a retry button

### Your use case

#### What would you like to do?
Being able to easily retry downloading an image I want to view.

Also, additionally, the message currently looks like it could easily be faked by the other side (and so, by extension, might come from a bridge than from Element). See this image as example:

#### Why would you like to do it?
Because it is not intuitive to first open another room to then go back for Element to retry downloading the failed images.

And because it would be easier to differentiate such errors from normal message flow.

#### How would you like to achieve it?
Adding a retry button beside the failed message.

Also restyle the message so it becomes clear to technical & non-technical users, that this message is not part of the normal message flow (compare to encryption errors)

This may be combined with supporting HTTP Range requests (see [MSC3469](https://github.com/matrix-org/matrix-spec-proposals/pull/3469) with further linked MSCs) to be able to continue failed downloads, which saves data and increases the likelihood of finishing the download successfully.

### Have you considered any alternatives?

Element might also implement an auto-retry mode (similar to what it currently does if the whole connection to the server fails), however this should really be combined with HTTP Range requests to reduce data usage.

### Additional context

If such error happens, it mostly happens (for me) on unsteady connections (travelling with a train, especially in Germany), hence this error does not happen often.

I've originally seen this message on SchildiChat (fork from Element), however looking into the differences, I conclude that this message should be looking the same on Element as of now, hency why I propose this here. Getting this error on will without knowing the internals of Element is (gracefully) not that easy, so I was not able to verify that SchildiChat & Element share this issue. If I'm wrong, sorry for the disturbance.