Make SegmentSelectorEditor tests less flaky

[caddoo]

Description

These screenshot tests were flaky for me (each failed at least once), likely due to hover/tooltips being captured.
This PR moves the mouse out of the capture area before taking the affected screenshots to stabilize them.

It also improves debugging clarity by splitting a shared baseline: two tests previously used updated.png, which made
failures harder to interpret (often showing no useful diff). The reload-step test now uses its own duplicated baseline
image so each assertion can fail independently with clearer output.

Failures addressed:
https://builds-artifacts.matomo.org/matomo-org/matomo/preview_alerts/22417472720/

https://builds-artifacts.matomo.org/matomo-org/matomo/segment_selector_editor_flaky/22423974975/

Checklist

• [✔] I have understood, reviewed, and tested all AI outputs before use
• [✔] All AI instructions respect security, IP, and privacy rules

Review

• Functional review done
• Potential edge cases thought about (behaviour of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• Security review done
• Wording review done
• Code review done
• Tests were added if useful/possible
• Reviewed for breaking changes
• Developer changelog updated if needed
• New documentation added or existing documentation updated