Investigate using looks-same instead of pixelmatch for visual tests

[web-padawan]

It appears that pixelmatch does not fully handle anti-aliasing, see mapbox/pixelmatch#74

We could consider using looks-same to compare screenshots (we used it through gemini before).
This would require the following steps:

1. write a custom diff function instead of pixelMatchDiff which comes out of the box
2. pass this custom function to @web/test-runner-visual-regression via getImageDiff config option.

If this would requires some refactoring to the plugin, we can submit an issue to Modern Web project.

[sissbruecker]

We closed this, as there are newer / more general tickets for fixing the visual tests. I tried the suggestion here, but it did not make a difference. After investigating it turns out both libraries use the same algorithm for anti-aliasing detection.