PhanTypeModifyImmutableObjectProperty should be emitted for any scope other than readonly property's class definition

[TysonAndre]

<?php
class X { public readonly int $x; }
// Should emit PhanTypeModifyImmutableObjectProperty. At runtime this throws
// > Error: Cannot initialize readonly property X::$x from scope Y
class Y extends X { public function __construct() { $this->x = 123; } }
$y = new Y();
// Emits PhanAccessReadOnlyProperty, should also emit PhanTypeModifyImmutableObjectProperty
$y->x = 123;