Implement lateinit in backend

compiler/testData/codegen/box/properties/lateinit/accessor.kt

@@ -0,0 +1,20 @@
+public class A {
+
+    fun setMyStr() {
+        str = "OK"
+    }
+
+    fun getMyStr(): String {
+        return str
+    }
+
+    private companion object {
+        private lateinit var str: String
+    }
+}
+
+fun box(): String {
+    val a = A()
+    a.setMyStr()
+    return a.getMyStr()
+}