[analyzer] canonicalize special case of structure/pointer deref

This simple change addresses a special case of structure/pointer
aliasing that produced different symbolvals, leading to false positives
during analysis.

The reproducer is as simple as this.

```lang=C++
struct s {
  int v;
};

void foo(struct s *ps) {
  struct s ss = *ps;
  clang_analyzer_dump(ss.v); // reg_$1<int Element{SymRegion{reg_$0<struct s *ps>},0 S64b,struct s}.v>
  clang_analyzer_dump(ps->v); //reg_$3<int SymRegion{reg_$0<struct s *ps>}.v>
  clang_analyzer_eval(ss.v == ps->v); // UNKNOWN
}
```

Acks: Many thanks to @steakhal and @martong for the group debug session.

Reviewed By: steakhal, martong

Differential Revision: https://reviews.llvm.org/D110625