Choose multiple files in Media

[KomAfdUmb]

Selecting multiple files in the Media folder currently requires clicking on the very edge of a file, which isn't intuitive and isn't visually indicated well.

To improve this, I suggest adding checkboxes or a similar visual element to make it easier to select multiple files and to clearly show that bulk selection is possible.

[marcemarc]

Linked to this: #18405

google-photos-selecting.mp4