Revert "Temporarily remove isInitialized and tests, but keep the implementation"

This reverts commit 234148518e.

compiler/testData/codegen/box/properties/lateinit/isInitializedAndDeinitialize/innerSubclass.kt

@@ -0,0 +1,35 @@
+// TARGET_BACKEND: JVM
+// LANGUAGE_VERSION: 1.2
+// WITH_RUNTIME
+
+open class Foo {
+    lateinit var bar: String
+
+    private lateinit var baz: String
+
+    fun test(): String {
+        val isBarInitialized: () -> Boolean = { this::bar.isInitialized }
+        if (isBarInitialized()) return "Fail 1"
+        bar = "bar"
+        if (!isBarInitialized()) return "Fail 2"
+        baz = "baz"
+        return InnerSubclass().testInner()
+    }
+
+    inner class InnerSubclass : Foo() {
+        fun testInner(): String {
+            // This is access to InnerSubclass.bar which is inherited from Foo.bar
+            if (this::bar.isInitialized) return "Fail 3"
+            bar = "OK"
+            if (!this::bar.isInitialized) return "Fail 4"
+
+            // This is access to Foo.bar declared lexically above
+            if (!this@Foo::bar.isInitialized) return "Fail 5"
+            return "OK"
+        }
+    }
+}
+
+fun box(): String {
+    return Foo().test()
+}