java completion: suggest only denotable method return types (IDEA-194462)

java/java-tests/testData/codeInsight/completion/smartType/SuggestMethodReturnTypeAnonymous.java

@@ -0,0 +1,7 @@
+public class Main {
+
+  public <caret>x main() {
+    return new Object(){};
+  }
+
+}