Responsive size for image upload dialogue

#### Is your suggestion related to a problem? Please describe.
The file upload dialogue previews an image to confirm upload. This dialogue is ridiculously small on a big screen - by far smaller than the thumbnail maximum.

Here is element fullscreen on a 1440p screen (minus browser + OS frame):

#### Describe the solution you'd like.
A more adequate size, responsive to the window size. It is probably reasonable to use the same size at which a thumbnail would display, as seen in the timeline in the background.

While at it, the dialogue could also show some basic info like dimension, duration, ... depending on media type.

#### Describe alternatives you've considered.
no

#### Additional context
no