Implement the actual snapping functionality

[swissspidy]

Feature description

While #3060 introduced visual snapping guidelines, we decided to back out the actual snapping feature as it didn't work well enough.

It's time to revisit this and to do implement this properly and only for the cases where it makes sense. For instance, perhaps snapping should be limited to dragging for now.

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Acceptance criteria

Implementation brief

QA testing instructions

Demo

Changelog entry