use mockJdk18 by default in LightCodeInsightTestCase; remove dependency on swing/net classes in some tests

java/java-tests/testData/refactoring/extractMethod/ExtractUnresolvedLambdaExpression_after.java

@@ -1,3 +1,5 @@
+import org.jetbrains.annotations.NotNull;
+
 import java.util.function.Supplier;
 class Test {
 
@@ -6,6 +8,7 @@ class Test {
     b(newMethod());
   }
 
+    @NotNull
     private Supplier newMethod() {
         return (s) -> {
           System.out.println(s);