ci: Parallelize visual specs

What does this MR do?

ci: Parallelize visual specs

Because why not

test: Expose more data from screenshot tests

1. Store the new screenshot as well and not just the diff. This means, we can simply copy paste a new screenshot over the old one. They are stored in tests/__image_snapshots__/__received_output__
2. New tests don't have a baseline screenshot, so the mechanism from 1. doesn't work for them. Given that we calculate the filenames of the screenshot file, we can simply smuggle in a template file, so that we always have a screenshot.
3. It is pretty tricky to know which screenshots to delete. With a sharded approach, we also would not run all screenshot tests at the same time, so we write out a file __seen_snapshots_ which contains all the screenshots the current shard has utilized.

ci: Remove visual_minimal job

Given we potentially want to move a job which updates screenshots based on the artifacts and that we now can scale visual screenshot tests horizontally, let's get rid of the minimal job.

Screenshots or screen recordings

N/A

Integration merge requests

None 😄

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