Inner classes lowering.

compiler/testData/ir/box/closureConversion/innerClass1.kt

@@ -0,0 +1,8 @@
+class Outer {
+    val x = "O"
+    inner class Inner {
+        val y = x + "K"
+    }
+}
+
+fun box() = Outer().Inner().y

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

@@ -0,0 +1,5 @@
+class Outer {
+    inner class Inner(val x: Int) {
+        constructor() : this(0)
+    }
+}

compiler/testData/ir/irText/classes/innerClassWithDelegatingConstructor.txt

@@ -0,0 +1,25 @@
+FILE /innerClassWithDelegatingConstructor.kt
+  CLASS CLASS Outer
+    CONSTRUCTOR public constructor Outer()
+      BLOCK_BODY
+        DELEGATING_CONSTRUCTOR_CALL 'constructor Any()'
+        INSTANCE_INITIALIZER_CALL classDescriptor='Outer'
+    CLASS CLASS Inner
+      CONSTRUCTOR public constructor Inner(x: kotlin.Int)
+        BLOCK_BODY
+          DELEGATING_CONSTRUCTOR_CALL 'constructor Any()'
+          INSTANCE_INITIALIZER_CALL classDescriptor='Inner'
+      PROPERTY public final val x: kotlin.Int
+        FIELD PROPERTY_BACKING_FIELD public final val x: kotlin.Int
+          EXPRESSION_BODY
+            GET_VAR 'value-parameter x: Int' type=kotlin.Int origin=INITIALIZE_PROPERTY_FROM_PARAMETER
+        FUN DEFAULT_PROPERTY_ACCESSOR public final fun <get-x>(): kotlin.Int
+          BLOCK_BODY
+            RETURN type=kotlin.Nothing from='<get-x>(): Int'
+              GET_FIELD 'x: Int' type=kotlin.Int origin=null
+                receiver: GET_VAR '<receiver: Inner>' type=Outer.Inner origin=null
+      CONSTRUCTOR public constructor Inner()
+        BLOCK_BODY
+          DELEGATING_CONSTRUCTOR_CALL 'constructor Inner(Int)'
+            $this: GET_VAR '<receiver: Outer>' type=Outer origin=null
+            x: CONST Int type=kotlin.Int value='0'