Allow use of selected text for filename when pasting images

[danyill]

Why the new feature should be added

It would be great if I had some selected text, then if when I pasted an image this text was the starting point for the image name.

My use case is that I sometimes run a set of tests where the image names are relatively long but the suffix on each is slightly different I end up re-typing the text in the box again and again.

The modal window that the image name screen opens up is also blocking, so I can't copy the text from the editor once it is open.

How the new feature should work

1. I would highlight some specific text in the editor.
2. I would then go Ctrl+V or click the image icon.

The save image would open and it would use the text I provided as the default text.

Ideally it would scrub "weird" characters using a whitelist of allowable characters for the OS platform.

This feature exists on the asciidoctor-vscode extension and I think it would be great here too.