[clang] Reland "[clang][Sema] Use original template pattern when declaring implicit deduction guides for nested template classes" (PR #69676)

[kadir çetinkaya via cfe-commits]

kadircet wrote:

thanks for the revert! I also encountered certain crashes bisecting back to this patch, with a similar reproducer:
```
template <class T>
struct Module {
  template <class... Bazs>
  struct Baz {
    template <class X, int Y = 0>
    explicit Baz(X);
  };
  Baz(int) -> Baz<int, char>;
};

struct Bar {};

void foo() { Module<Bar>::Baz x{2}; }
```

https://github.com/llvm/llvm-project/pull/69676