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/sam/adapters/inheritance/InheritedSimple.fir.txt

@@ -1,2 +1,8 @@
 public abstract interface InheritedSimple : R|kotlin/Any| {
+    public abstract interface Sub : R|test/InheritedSimple.Super| {
+    }
+    public abstract interface Super : R|kotlin/Any| {
+        public abstract fun foo(r: R|ft<java/lang/Runnable, java/lang/Runnable?>|): R|kotlin/Unit|
+
+    }
 }