Disable relevance reduction of Closure methods and properties when object expression type is Closure

[eric-milles]

Consider the following:

void meth(Closure closure) {
  closure.|
}

When invoking content assist (Ctrl+Space) at |, the methods and properties of groovy.lang.Closure are very low in the list of proposals. This is due to very-well-known type adjustments made within org.codehaus.groovy.eclipse.codeassist.proposals.AbstractGroovyProposal.getRelevanceClass().