Add a from_u32 function to EntityRef.

This eliminates the need for casting in common cases.

lib/entity/src/lib.rs

@@ -100,6 +100,13 @@ macro_rules! entity_impl {
         }
 
         impl $entity {
+            /// Return the underlying index value as a `u32`.
+            #[allow(dead_code)]
+            pub fn from_u32(x: u32) -> Self {
+                debug_assert!(x < $crate::__core::u32::MAX);
+                $entity(x)
+            }
+
             /// Return the underlying index value as a `u32`.
             #[allow(dead_code)]
             pub fn as_u32(self) -> u32 {