[IR] dumpKotlinLike: add testdata for FIR tests

compiler/testData/ir/irText/expressions/whenUnusedExpression.fir.kt.txt

@@ -0,0 +1,12 @@
+fun test(b: Boolean, i: Int) {
+  when {
+    b -> { // BLOCK
+      val tmp0_subject: Int = i
+      when {
+        EQEQ(arg0 = tmp0_subject, arg1 = 0) -> 1
+        else -> null
+      }
+    }
+    else -> null
+  } /*~> Unit */
+}