Represent class instance initialization "as from resolve".

compiler/testData/ir/irText/classes/initBlock.kt

@@ -0,0 +1,31 @@
+class Test1 {
+    init {
+        println()
+    }
+}
+
+class Test2(val x: Int) {
+    init {
+        println()
+    }
+}
+
+class Test3 {
+    init {
+        println()
+    }
+
+    constructor()
+}
+
+class Test4 {
+    init {
+        println("1")
+    }
+
+    constructor()
+
+    init {
+        println("2")
+    }
+}