Introduce KProperty{1,2}.getExtensionDelegate

These two functions are supposed to fix an inconvenience in the design of
KProperty{1,2}.getDelegate for extension properties, where you have to pass an
instance of the extension receiver which is going to be completely ignored

 #KT-8384 Fixed

compiler/testData/codegen/box/reflection/properties/getDelegate/getExtensionDelegate.kt

@@ -0,0 +1,38 @@
+// IGNORE_BACKEND: JS
+// WITH_REFLECT
+
+import kotlin.reflect.KProperty
+import kotlin.reflect.KProperty2
+import kotlin.reflect.jvm.isAccessible
+import kotlin.reflect.full.getExtensionDelegate
+import kotlin.test.*
+
+object Delegate {
+    operator fun getValue(instance: Any?, property: KProperty<*>) = true
+}
+
+class Foo {
+    val member: Boolean by Delegate
+    val String.memberExtension: Boolean by Delegate
+}
+
+val Foo.extension: Boolean by Delegate
+
+fun box(): String {
+    // Top level extension
+    assertEquals(Delegate, Foo::extension.apply { isAccessible = true }.getExtensionDelegate())
+
+    // Member extension
+    val me = Foo::class.members.single { it.name == "memberExtension" } as KProperty2<Foo, String, Boolean>
+    assertEquals(Delegate, me.apply { isAccessible = true }.getExtensionDelegate(Foo()))
+
+    // Member (should fail)
+    try {
+        Foo::member.apply { isAccessible = true }.getExtensionDelegate()
+        return "Fail: getExtensionDelegate() should fail on a non-extension property"
+    } catch (e: Exception) {
+        // OK
+    }
+
+    return "OK"
+}