 Raw read view supports the `count` method now


Since: 3.8.0

Raw read views (ones that can be used from C API) are popualted
with count method now:

```c
API_EXPORT ssize_t
box_raw_read_view_count(const box_raw_read_view_index_t *index, int type,
			const char *key, const char *key_end);

```
Requested by @drewdzzz in https://github.com/tarantool/tarantool-ee/commit/c818144a19005095efc0fdd1c0e2cc946a521e8b.