Add the function body span to StableMIR

compiler/rustc_smir/src/rustc_smir/convert/mir.rs

@@ -37,6 +37,7 @@ impl<'tcx> Stable<'tcx> for mir::Body<'tcx> {
             self.arg_count,
             self.var_debug_info.iter().map(|info| info.stable(tables)).collect(),
             self.spread_arg.stable(tables),
+            self.span.stable(tables),
         )
     }
 }