transpile: const macros: do not resolve expr type

resolving the type ignores all casts, but some casts are nontrivial computations that we cannot elide, e.g. truncating larger types to smaller ones

as far as I'm aware we can simply not resolve the expression type here; we'll emit more casts in these cases, but some of those may be load-bearing

Author: fw-immunant

c2rust-transpile/src/translator/mod.rs

@@ -2174,11 +2174,8 @@ impl<'c> Translation<'c> {
                     .kind
                     .get_type()
                     .ok_or_else(|| format_err!("Invalid expression type"))?;
-                let (expr_id, ty) = self
-                    .ast_context
-                    .resolve_expr_type_id(id)
-                    .unwrap_or((id, ty));
-                let expr = self.convert_expr(ctx, expr_id, None)?;
+                let ty = self.ast_context[id].kind.get_type().unwrap_or(ty);
+                let expr = self.convert_expr(ctx, id, None)?;
 
                 // Join ty and cur_ty to the smaller of the two types. If the
                 // types are not cast-compatible, abort the fold.