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/ArrayInGenericArguments.fir.txt

@@ -7,4 +7,8 @@ public open class ArrayInGenericArguments : R|kotlin/Any| {
 
     public constructor(): R|ArrayInGenericArguments|
 
+    public open class DataKey<T : R|ft<kotlin/Any, kotlin/Any?>|> : R|kotlin/Any| {
+        public constructor<T : R|ft<kotlin/Any, kotlin/Any?>|>(): R|ArrayInGenericArguments.DataKey<T>|
+
+    }
 }