[clang] [Sema] Fast-path simple plain auto deduction in DeduceAutoType (PR #188196)

[via cfe-commits]

https://github.com/Sirraide commented:

Can you add some more tests involving e.g. `auto *const`, `auto *__restrict`, e.g.
```c++
const int* p1;
auto* __restrict x1 = p1;
static_assert(__is_same(decltype(x1), const int *__restrict));

volatile int* p2;
auto* const x2 = p2;
static_assert(__is_same(decltype(x2), volatile int *const));

volatile int* __restrict p3;
const auto* const x3 = p3;
static_assert(__is_same(decltype(x3), volatile const int * const));
```

https://github.com/llvm/llvm-project/pull/188196