[C-API] - add support for Dictionary::get_keys(), Dictionary::contains(StringData key) and Dictionary::find_any(Mixed value)

[edualonso]

Kotlin exposes keys, containsKey(key: K) and containsValue(value: V) in its Map interface so we need the following functions (or similar) to be added to the C-API:

• Dictionary::get_keys()->realm_dictionary_get_keys(const realm_dictionary_t*, size_t* out_size, realm_value_t* out_keys)
• Dictionary::contains(StringData key)->realm_dictionary_contains_key(const realm_dictionary_t*, realm_value_t key)
• Dictionary::find_any(Mixed value)->realm_dictionary_contains_value(const realm_dictionary_t*, realm_value_t value)

[edualonso]

Is it possible to also get size_t* out_index for realm_dictionary_contains_key and realm_dictionary_contains_value? I have found a use case where it would be very beneficial to receive the position in which the key or value are located. Not super important though, it would make my life a bit easier 😅

[edualonso]

I don't think I need out_index for keys and values after all.