update jdt.core to I20210804-1800 (around skipped M2)

incl.
- a few version updates
- refresh of otdt.AbstractJavaModelTests
- fup from migration StringBuffer -> StringBuilder
- fup from updated JavaElement.getParent() et al
- adjust AstGenerator.caseStatement(): null -> new Expression[0]

Change-Id: If281404cced772094319e69d89e4e5a59dee37fe
diff --git a/org.eclipse.jdt.core.tests.model/.classpath b/org.eclipse.jdt.core.tests.model/.classpath
index 7c258d5..3281193 100644
--- a/org.eclipse.jdt.core.tests.model/.classpath
+++ b/org.eclipse.jdt.core.tests.model/.classpath
@@ -1,5 +1,9 @@
 <classpath>
-	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8"/>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-11">
+		<attributes>
+			<attribute name="module" value="true"/>
+		</attributes>
+	</classpathentry>
 	<classpathentry kind="con" path="org.eclipse.pde.core.requiredPlugins"/>
 	<classpathentry kind="src" path="src">
 		<attributes>