Save screenshot (screen / rect) to storage pool and to stdin

[christianparpart]

I know there is mediacopy (See https://github.com/hackerb9/vt340test/blob/main/mediacopy/mediacopy.sh).
But this feels rather complex to me and I wonder if that could be very much trivialized into one or two simple VT sequences with only few parameters.

Idea is:

• save screenshot (of full screen or screen cell region) and receive it through stdin
• save screenshot (of full screen or screen cell region) and upload it to the storage pool with a given name

It should be possible to operate on the full screen with and without padding as well as on only a region of the screen, using screen cell coordinates.

Question is whether that should be possible to take a screenshot of the scrollback area or not. This sounds like something that the user would probably want to have configurable anyways.