Theme: remove dependency on Theme attached property from Constants #19485
Description
Description
Constants, as the name says, should contain static, read-only content. Currently there is dependency on Theme attached property, which brings state into that component. It's problematic in a singleton as it's top-level component and doesn't follow normal rules regarding propagation. The workaround in main.qml was created to propagate from top-level window to the singleton.
The goal is to refactor Constants and remove the dependency on Theme.
Follow up of #19213