use getResolvedClasspathEntry directly

See eclipse/Xpect#353 #3123

org.eclipse.xtext.xbase.ui/src/org/eclipse/xtext/xbase/ui/validation/XbaseUIValidator.java

@@ -26,7 +26,6 @@
 import org.eclipse.jdt.core.JavaModelException;
 import org.eclipse.jdt.core.compiler.CharOperation;
 import org.eclipse.jdt.internal.core.ClasspathAccessRule;
-import org.eclipse.jdt.internal.core.JavaProject;
 import org.eclipse.xtext.common.types.JvmConstructor;
 import org.eclipse.xtext.common.types.JvmDeclaredType;
 import org.eclipse.xtext.common.types.JvmIdentifiableElement;
@@ -219,17 +218,6 @@ protected RestrictionKind computeRestriction(IJavaProject project, IType type) {
 
 	/* @Nullable */ 
 	protected IClasspathEntry getResolvedClasspathEntry(IJavaProject javaProject, /* @NonNull */ IPackageFragmentRoot root) throws JavaModelException {
-		IClasspathEntry result = null;
-		JavaProject castedProject = (JavaProject) javaProject;
-		castedProject.getResolvedClasspath(); // force the resolved entry cache to be populated
-		@SuppressWarnings("rawtypes")
-		Map rootPathToResolvedEntries = castedProject.getPerProjectInfo().rootPathToResolvedEntries;
-		if (rootPathToResolvedEntries != null) {
-			result = (IClasspathEntry) rootPathToResolvedEntries.get(root.getPath());
-			if (result == null)
-				result = (IClasspathEntry) rootPathToResolvedEntries.get(root.getJavaProject().getPath());
-		}
-
-		return result;
+		return root.getResolvedClasspathEntry();
 	}
 }