effects/screenshot: Backport CaptureWorkspace method and screen, windowId and scale properties to 5.27
These are technically new features, but they don't seem to require translatable strings, they're not disruptive changes and they're necessary for fixing Spectacle bugs under Plasma 5.27.
I actually only need the patches for screen, windowId and scale, but I thought it might be a good idea to include CaptureWorkspace as well. Without it, the version for the screenshot API would jump from 2 to 4, skipping what was added in version 3. That sounds like a recipe for trouble.