Add expand+crop tooling to the UI screenshot taker used for documentation

[adamkewley]

Estimate: 1-2d (incl. tagging relevant popups etc.)

When taking documentation screenshots, I regularly have to crop out parts of the screen (e.g. popups) and highlight them etc. - it's very time-consuming to flip between various applications etc.

OSC currently have a screenshot-taker. Later iterations added the ability to tag parts of the screen with red boxes. This issue addresses also cropping the image.

[adamkewley]

Dropping from 0.4.1 - there's been other bugfixes etc. popping up and there won't be time to also integrate this before the release window.