Hover feedback is not working when using the EdgeCreationTool

[tortmayr]

When the EdgeCreationTool is active, hover feedback does not work.
This is caused by the the check in this GLSPHoverMouseListener:
https://github.com/eclipse-glsp/glsp-client/blob/2d240a399693676cd7ac2b3740f95f4b6562f3ad/packages/client/src/features/hover/hover.ts#L58

Affectingly the hover listener is completely disabled when the EdgeCreationTool is active. I think the intention behind this was to avoid hover popup computation during edge creation. While we definitely should do that, the hover Feedback should still be active (or at least it should be configurable).
The hover feedback provides a nice visual indicator about the current target/source candidate.

In addition, we should find a cleaner solution instead of hardcoding the disablement into the GLSPHoverTool. This creates an indirect dependency between the hoverModule and the edgeCreationModule.