proper widgetid + slot vec instead of map

core/src/util/mod.rs

@@ -1,6 +1,7 @@
 mod arena;
 mod borrow;
 mod change;
+mod slot;
 mod id;
 mod math;
 mod refcount;
@@ -9,6 +10,7 @@ mod vec2;
 pub use arena::*;
 pub use borrow::*;
 pub use change::*;
+pub use slot::*;
 pub use id::*;
 pub use math::*;
 pub use refcount::*;