Remove CanvasTestSetup dependency from CanvasFieldTrait and test-discovery guard

Wim Leersrequested to merge
issue/canvas-3531679:3531679-decouple-kerneltests-from-canvastestsetup into 1.x

🚨 NOT ready for review. Wanted to see the test results on CI.

AI-Generated: Yes.

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Closes #3531679

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