chore: remove platform WindowId's

WindowId is a window _identifier_, and as such doesn't store anything
(unlike a _handle_). So we can safely make only be defined once, in the
core crate.

There are a few backends where we still use `into_raw` internally; I
consider these patterns discouraged, we should not be passing around
important state in the window id.

src/platform_impl/orbital/mod.rs

@@ -99,21 +99,6 @@ impl TimeSocket {
 #[derive(Default, Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub(crate) struct PlatformSpecificEventLoopAttributes {}
 
-#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
-pub struct WindowId {
-    fd: u64,
-}
-
-impl WindowId {
-    pub const fn into_raw(self) -> u64 {
-        self.fd
-    }
-
-    pub const fn from_raw(id: u64) -> Self {
-        Self { fd: id }
-    }
-}
-
 #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
 pub struct DeviceId;