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/annotations/AnnotatedMethod.fir.txt

@@ -3,4 +3,8 @@ public open class AnnotatedMethod : R|kotlin/Any| {
 
     public constructor(): R|test/AnnotatedMethod|
 
+    public final annotation class Anno : R|kotlin/Annotation| {
+        public constructor(value: R|kotlin/Int|): R|test/AnnotatedMethod.Anno|
+
+    }
 }