Update jdt.core to I20210503-1800

* re-fix https://bugs.eclipse.org/bugs/show_bug.cgi?id=561820#c12 (JDT)
* more re: improve/differentiate keyword completion
  - revert previous test adjustments
* update tests to JavaSE-11, to match the BREE of o.e.equinox.common
diff --git a/testplugins/org.eclipse.objectteams.otdt.test.builder/workspace/UnresolvedBasePlugin/META-INF/MANIFEST.MF b/testplugins/org.eclipse.objectteams.otdt.test.builder/workspace/UnresolvedBasePlugin/META-INF/MANIFEST.MF
index 211d4ae..4a2d531 100644
--- a/testplugins/org.eclipse.objectteams.otdt.test.builder/workspace/UnresolvedBasePlugin/META-INF/MANIFEST.MF
+++ b/testplugins/org.eclipse.objectteams.otdt.test.builder/workspace/UnresolvedBasePlugin/META-INF/MANIFEST.MF
@@ -7,5 +7,5 @@
 Require-Bundle: org.eclipse.objectteams.otequinox,
  org.eclipse.objectteams.runtime
 Bundle-ActivationPolicy: lazy
-Bundle-RequiredExecutionEnvironment: JavaSE-1.8
+Bundle-RequiredExecutionEnvironment: JavaSE-11
 Export-Package: pack