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ARROW-13097: [C++] Provide simple reflection utility

Provides functions for enumerating struct's data members, which enables reduction of boilerplate since many operations (equality comparison, serialization, ...) can be reduced to a generic loop over this enumeration of members.

```c++
struct Person { int age; std::string name; };

static auto kPersonProperties =
    MakeProperties(DataMember("age", &Person::age), DataMember("name", &Person::name));

bool operator==(const Person& l, const Person& r) { return EqualsImpl<Person>{l, r, kPersonProperties}.equal_; }
```

Closes #10551 from bkietz/13097-Provide-a-simple-reflecti

Authored-by: Benjamin Kietzman <bengilgit@gmail.com>
Signed-off-by: Benjamin Kietzman <bengilgit@gmail.com>