[xtext][ui] Fixed race in editor / coloring

Newly opened editors are forced to be reconciled
which could have lead to duplicate position due
to a race in the highlighting reconciler

see https://xtext-builds.itemis.de/jenkins/job/xtend-slow-tests-Latest/816/testReport/junit/org.eclipse.xtend.ide.tests.highlighting/HighlightingReconcilerTest/testNoSematicHighlightingOnOpen/

Change-Id: Ibcfa8baec06c18932d4c0a9bdb417a9cec057386
Fix failing test that runs green locally but not on the server
Merge "[xtext][ui] Fixed race in editor / coloring"
Merge "Fix failing test that runs green locally but not on the server"