FIR: dump nested classes in loadJava tests

Because those test are single Java files, many of them use a top-level
class as a container for multiple classes to be tested. Such tests do
almost nothing if those nested classes aren't handled.

compiler/testData/loadJava/compiledJava/NestedClass.fir.txt

@@ -1,4 +1,8 @@
 public open class NestedClass : R|kotlin/Any| {
     public constructor(): R|test/NestedClass|
 
+    public open class Nested : R|kotlin/Any| {
+        public constructor(): R|test/NestedClass.Nested|
+
+    }
 }