JVM: add tests for optimized getDelegate

compiler/testData/codegen/box/delegatedProperty/delegateToAnotherCustom.kt

@@ -0,0 +1,14 @@
+// WITH_RUNTIME
+var x: String
+    get() = throw Exception("x's getter shouldn't be called")
+    set(_) { throw Exception("x's setter shouldn't be called") }
+var y: String by ::x
+
+var storage = "Fail"
+operator fun Any.getValue(thiz: Any?, property: Any?): String = storage
+operator fun Any.setValue(thiz: Any?, property: Any?, value: String) { storage = value }
+
+fun box(): String {
+    y = "OK"
+    return y
+}

compiler/testData/codegen/box/delegatedProperty/delegateToAnotherReflection.kt

@@ -0,0 +1,51 @@
+// WITH_REFLECT
+// TARGET_BACKEND: JVM
+import kotlin.reflect.*
+import kotlin.reflect.jvm.isAccessible
+import kotlin.reflect.full.getExtensionDelegate
+
+class C(var x: Int) {
+    var y by C::x
+    var z by ::x
+}
+
+class D(val c: C) {
+    var y by c::x
+}
+
+var x = 1
+var y by ::x
+var z by C(1)::x
+
+var _x = -99
+var Int.x
+    get() = this + _x
+    set(v: Int) { _x = v - this }
+var Int.y by Int::x
+
+inline fun <P : KProperty<*>, R> P.test(delegate: P.() -> R, get: R.() -> Int, set: R.(Int) -> Unit) {
+    val ref = apply { isAccessible = true }.delegate()
+    require(ref.get() == 1) { "$ref initial value is ${ref.get()}, not 1" }
+    ref.set(2)
+    require(ref.get() == 2) { "$ref after set(2) is ${ref.get()}, not 2" }
+    ref.set(1)
+}
+
+fun KMutableProperty0<Int>.test() =
+    test({ getDelegate() as KMutableProperty0<Int> }, { get() }, { set(it) })
+
+fun <T> KMutableProperty1<T, Int>.test(receiver: T) =
+    test({ getDelegate(receiver) as KMutableProperty0<Int> }, { get() }, { set(it) })
+
+fun <T> KMutableProperty1<T, Int>.test(receiver: T, receiver2: T) =
+    test({ getDelegate(receiver) as KMutableProperty1<T, Int> }, { get(receiver2) }, { set(receiver2, it) })
+
+fun box(): String {
+    C::y.test(C(100), C(1))
+    C::z.test(C(1))
+    D::y.test(D(C(1)))
+    ::y.test()
+    ::z.test()
+    Int::y.test({ getExtensionDelegate() as KMutableProperty1<Int, Int> }, { get(100) }, { set(100, it) })
+    return "OK"
+}