Make DeviceId/WindowId::dummy() safe (#3784)

src/platform_impl/apple/uikit/mod.rs

@@ -31,7 +31,7 @@ pub(crate) use crate::platform_impl::Fullscreen;
 pub struct DeviceId;
 
 impl DeviceId {
-    pub const unsafe fn dummy() -> Self {
+    pub const fn dummy() -> Self {
         DeviceId
     }
 }

src/platform_impl/apple/uikit/window.rs

@@ -699,7 +699,7 @@ pub struct WindowId {
 }
 
 impl WindowId {
-    pub const unsafe fn dummy() -> Self {
+    pub const fn dummy() -> Self {
         WindowId { window: std::ptr::null_mut() }
     }
 }