8310314: Misplaced "unnamed classes are a preview feature and are disabled by default" error

Reviewed-by: jlaskey

test/langtools/tools/javac/unnamedclass/SourceLevelErrorPosition.java

@@ -0,0 +1,13 @@
+/**
+ * @test /nodynamiccopyright/
+ * @bug 8310314
+ * @summary Ensure proper error position for the "unnamed classes not supported" error
+ * @compile/fail/ref=SourceLevelErrorPosition.out -XDrawDiagnostics SourceLevelErrorPosition.java
+ */
+class Nested {}
+void main() {
+    System.err.println("");
+}
+void test() {
+    System.err.println("");
+}