KT-52592 Fix NPE from KProperty.getExtensionDelegate on property delegated to another property; make $delegate methods private

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

@@ -0,0 +1,16 @@
+// TARGET_BACKEND: JVM
+// WITH_REFLECT
+
+import kotlin.reflect.full.getExtensionDelegate
+import kotlin.reflect.jvm.isAccessible
+import kotlin.test.assertEquals
+
+class A
+
+val A.x: Int get() = 1
+val A.y: Int by A::x
+
+fun box(): String {
+    assertEquals(A::x, A::y.apply { isAccessible = true }.getExtensionDelegate())
+    return "OK"
+}

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

@@ -11,11 +11,15 @@ object Delegate {
 }
 
 val topLevel: Boolean by Delegate
+val delegated: Boolean by ::topLevel
 val String.extension: Boolean by Delegate
+val String.delegated: Boolean by String::delegated
 
 class Foo {
     val member: Boolean by Delegate
+    val delegated: Boolean by ::member
     val String.memberExtension: Boolean by Delegate
+    val String.memberExtensionDelegated: Boolean by ::member
 }
 
 inline fun check(block: () -> Unit) {
@@ -29,16 +33,24 @@ inline fun check(block: () -> Unit) {
 
 fun box(): String {
     check { ::topLevel.getDelegate() }
+    check { ::delegated.getDelegate() }
 
     check { String::extension.getDelegate("") }
     check { ""::extension.getDelegate() }
+    check { String::delegated.getDelegate("") }
+    check { ""::delegated.getDelegate() }
 
     val foo = Foo()
     check { Foo::member.getDelegate(foo) }
     check { foo::member.getDelegate() }
+    check { Foo::delegated.getDelegate(foo) }
+    check { foo::delegated.getDelegate() }
 
     val me = Foo::class.members.single { it.name == "memberExtension" } as KProperty2<Foo, String, Boolean>
     check { me.getDelegate(foo, "") }
 
+    val med = Foo::class.members.single { it.name == "memberExtensionDelegated" } as KProperty2<Foo, String, Boolean>
+    check { med.getDelegate(foo, "") }
+
     return "OK"
 }