Remove important from sprotty css

[haydar-metin]

What it does

Works on eclipse-glsp/glsp#1241

• TODO: REMOVE MOVEMENT RESTRICTION BEFORE MERGE
  • It will fix the failing test

How to test

• Trigger validation
• Move a node to be above another node

Follow-ups

Changelog

• This PR should be mentioned in the changelog
• This PR introduces a breaking change (if yes, provide more details below for the changelog and the migration guide)

[tortmayr]

Changes look good to me and for the client/standalone example everything seems to work.
However, I quickly tested the change with the theia-integration an there the movement restriction feedback for routing handles is no longer properly applied:

With removing the !important it seems that another rule replaces the fill of the routing handles.
We should probably merge this and then retest the different integrations separately.

[haydar-metin]

@tortmayr thanks! I will now fix those integrations.