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/PrivateMembers.fir.txt

@@ -9,4 +9,14 @@ public open class PrivateMembers : R|kotlin/Any| {
 
     private constructor(): R|test/PrivateMembers|
 
+    private open inner class Inner : R|kotlin/Any| {
+        private constructor(): R|test/PrivateMembers.Inner|
+
+    }
+    private open class Nested : R|kotlin/Any| {
+        private open static fun staticMethodInNested(): R|kotlin/Unit|
+
+        private constructor(): R|test/PrivateMembers.Nested|
+
+    }
 }