[Clang] Accepts invalid reference declarator in type-id

The type-id uses a nested reference declarator &(&), which forms a reference to a reference. GCC rejects it, while Clang accepts it.
Code:

```c++
using X1 = union { } & ( & ) ;
```

See Compiler Explorer: [https://godbolt.org/z/fcv8zYh6Y](https://godbolt.org/z/fcv8zYh6Y)

The test case was generated by a fuzzer.

Reproduce the nested reference declarator in Clang using the provided C++ snippet, and compare its acceptance with GCC via the linked Compiler Explorer example. Trace the parser and type-id handling for `&(&)` and add a regression test showing that this invalid reference-to-reference form is rejected.

Written by the indexing model from the issue text.