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/PrivateMembersInHierarchy.fir.txt

@@ -1,4 +1,22 @@
 public open class PrivateMembersInHierarchy : R|kotlin/Any| {
     public constructor(): R|test/PrivateMembersInHierarchy|
 
+    public open class Sub : R|test/PrivateMembersInHierarchy.Super| {
+        private open field field: R|kotlin/Int|
+
+        private open fun method(): R|kotlin/Unit|
+
+        public constructor(): R|test/PrivateMembersInHierarchy.Sub|
+
+    }
+    public open class Super : R|kotlin/Any| {
+        private open field field: R|kotlin/Int|
+
+        private open field field2: R|kotlin/Int|
+
+        private open fun method(): R|kotlin/Unit|
+
+        public constructor(): R|test/PrivateMembersInHierarchy.Super|
+
+    }
 }