Cranelift: Derive Copy for InstructionData (#5043)

* Cranelift: Derive `Copy` for `InstructionData`

And update `clone` calls to be copies.

* Add a test for `InstructionData`'s size

cranelift/codegen/src/ir/function.rs

@@ -386,7 +386,7 @@ impl FunctionStencil {
             .zip(self.dfg.inst_results(src))
             .all(|(a, b)| self.dfg.value_type(*a) == self.dfg.value_type(*b)));
 
-        self.dfg[dst] = self.dfg[src].clone();
+        self.dfg[dst] = self.dfg[src];
         self.layout.remove_inst(src);
     }