[java-emf-theia] Label id generation is unstable

[tortmayr]

As discovered in https://github.com/eclipse-glsp/glsp-examples/pull/135#pullrequestreview-1052349434 the label ids in the java-emf-theia project template are unstable (i.e. a new id is assigned after each update) which results in animation flickering on each model updates.

[planger]

@xai is looking into that.