show image thumbnail in upload dialog

[williamkray]

Describe the problem

When sending an image, the upload progress dialog shows the name of the file and a generic image icon. when sending images from clipboard contents, the image is usually called something generic like image.png and so there are no opportunities to validate that the image you're about to post to matrix is in fact the one you think it is, or if you've just pasted in something you forgot was in your clipboard.

Describe the solution you'd like

it would be nice to have the image upload dialog show a small thumbnail of the actual image contents rather than a generic image icon.

Alternatives considered

never paste things from clipboard contents, and always name files uniquely

Additional context

No response