Put GetWeight where it belongs (#1212)

* Put `GetWeight` where it belongs

* add GetWeight to v2

* Re-export unchanged trait

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Co-authored-by: Just van Stam <just.van.stam@gmail.com>
Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>

polkadot/xcm/src/v2/traits.rs

@@ -23,6 +23,11 @@ use scale_info::TypeInfo;
 
 use super::*;
 
+// A simple trait to get the weight of some object.
+pub trait GetWeight<W> {
+	fn weight(&self) -> sp_weights::Weight;
+}
+
 #[derive(Copy, Clone, Encode, Decode, Eq, PartialEq, Debug, TypeInfo)]
 pub enum Error {
 	// Errors that happen due to instructions being executed. These alone are defined in the