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/enum/EnumWithSpecializedEntry.fir.txt

@@ -7,4 +7,8 @@ public final enum class EnumWithSpecializedEntry : R|kotlin/Enum<ft<test/EnumWit
     public final static fun valueOf(value: R|kotlin/String|): R|test/EnumWithSpecializedEntry| {
     }
 
+    public/*package*/ open class Nested : R|kotlin/Any| {
+        public/*package*/ constructor(): R|test/EnumWithSpecializedEntry.Nested|
+
+    }
 }