Detect bare blocks with type ascription that were meant to be a struct literal

Address part of #34255.

Potential improvement: silence the other knock down errors in
`issue-34255-1.rs`.

compiler/rustc_expand/src/build.rs

@@ -197,6 +197,7 @@ impl<'a> ExtCtxt<'a> {
             rules: BlockCheckMode::Default,
             span,
             tokens: None,
+            could_be_bare_literal: false,
         })
     }