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/Nested.fir.txt

@@ -1,2 +1,20 @@
 public abstract interface Nested : R|kotlin/Any| {
+    public abstract interface Deeper1 : R|kotlin/Any| {
+        public abstract interface Runnable : R|kotlin/Any| {
+            public abstract fun run(): R|kotlin/Unit|
+
+            public abstract fun run2(): R|kotlin/Unit|
+
+        }
+    }
+    public abstract interface Deeper2 : R|kotlin/Any| {
+        public abstract interface Runnable : R|kotlin/Any| {
+            public abstract fun run(): R|kotlin/Unit|
+
+        }
+    }
+    public abstract interface Runnable : R|kotlin/Any| {
+        public abstract fun run(): R|kotlin/Unit|
+
+    }
 }