wasmtime-slab: add PartialOrd and Ord to Ids. (#10568)

This became necessary in a use-case where I am using slab IDs as keys
in a BTreeMap (as a member of a tuple key type). The actual ordering
doesn't carry a fundamental meaning, but overall I do need ordering as
the first elements of the tuple have significant ordering and I need to
process in order (namely: timer deadlines). The slab ID ordering is at
least stable (since the Ids are integers under the hood), and this is
useful for anyone who needs to build an ordered key type. The
alternative is to use `.into_raw()` and manually write an `Ord` impl or
use the raw `u32` in a key, which is much worse.

Author: cfallin

crates/slab/src/lib.rs

@@ -131,7 +131,7 @@ use core::fmt;
 use core::num::NonZeroU32;
 
 /// An identifier for an allocated value inside a `slab`.
-#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[repr(transparent)]
 pub struct Id(EntryIndex);
 
@@ -193,7 +193,7 @@ enum Entry<T> {
     },
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[repr(transparent)]
 struct EntryIndex(NonZeroU32);