Prevent impossible combinations in ast::ModKind.

`ModKind::Loaded` has an `inline` field and a `had_parse_error` field.
If the `inline` field is `Inline::Yes` then `had_parse_error` must be
`Ok(())`.

This commit moves the `had_parse_error` field into the `Inline::No`
variant. This makes it impossible to create the nonsensical combination
of `inline == Inline::Yes` and `had_parse_error = Err(_)`.

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1169,7 +1169,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     self.dcx().emit_err(errors::UnsafeItem { span, kind: "module" });
                 }
                 // Ensure that `path` attributes on modules are recorded as used (cf. issue #35584).
-                if !matches!(mod_kind, ModKind::Loaded(_, Inline::Yes, _, _))
+                if !matches!(mod_kind, ModKind::Loaded(_, Inline::Yes, _))
                     && !attr::contains_name(&item.attrs, sym::path)
                 {
                     self.check_mod_file_item_asciionly(*ident);