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/static/InnerClass.fir.txt

@@ -1,4 +1,16 @@
 public open class InnerClass : R|kotlin/Any| {
     public constructor(): R|test/InnerClass|
 
+    public open inner class Inner : R|kotlin/Any| {
+        public open fun foo(): R|kotlin/Unit|
+
+        public constructor(): R|test/InnerClass.Inner|
+
+    }
+    public open class Nested : R|kotlin/Any| {
+        public open fun bar(): R|kotlin/Unit|
+
+        public constructor(): R|test/InnerClass.Nested|
+
+    }
 }