Record proc macro harness order for use during metadata deserialization

Fixes #68690

When we generate the proc macro harness, we now explicitly recorder the
order in which we generate entries. We then use this ordering data to
deserialize the correct proc-macro-data from the crate metadata.

src/librustc_parse/parser/module.rs

@@ -35,6 +35,8 @@ impl<'a> Parser<'a> {
             attrs: self.parse_inner_attributes()?,
             module: self.parse_mod_items(&token::Eof, lo)?,
             span: lo.to(self.token.span),
+            // Filled in by proc_macro_harness::inject()
+            proc_macros: Vec::new(),
         });
         krate
     }