Add labels for extension properties

#KT-2824 Fixed

compiler/testData/codegen/label/propertyAccessorInnerExtensionFun.kt

@@ -0,0 +1,27 @@
+val Int.getter: Int
+    get() {
+        val extFun = { Int.() ->
+            this@getter
+        }
+        return this@getter.extFun()
+    }
+
+
+var Int.setter: Int = 1
+    set(i: Int) {
+        val extFun = { Int.() ->
+            this@setter
+        }
+        this@setter.extFun()
+    }
+
+
+fun box(): String {
+    val i = 1
+    if (i.getter != 1) return "getter failed"
+
+    i.setter = 1
+    if (i.setter != 1) return "setter failed"
+
+    return "OK"
+}