[FIR] Assume nullable types as good types for ILT approximation

#KT-41982 Fixed

compiler/fir/analysis-tests/testData/resolve/delegates/kt41982.kt

@@ -0,0 +1,17 @@
+// ISSUE: KT-41982
+
+import kotlin.reflect.KProperty
+
+class Delegate<R, T> {
+    operator fun getValue(thisRef: R, property: KProperty<*>): T = null!!
+
+    operator fun setValue(thisRef: R, property: KProperty<*>, value: T) {}
+}
+
+abstract class DelegateProvider<in Type>
+
+fun <Type : Base, Base : DelegateProvider<Base>> Type.long(initializer: (() -> Long?)? = null): Delegate<Type, Long> = null!!
+
+class Test : DelegateProvider<Any>() {
+    var start by long { 0 }
+}