vinyl: cleanup range/index version usage
vinyl: cleanup range/index version usage

 - Rename vy_index->range_index_version => ->version
          vy_range->range_version => ->version
          vy_merge_iterator->range_index_version => ->index_version
 - Add a comment to vy_range->version
 - Do not increment vy_index->version on dump/compact in case only
   mem/run is added/removed and range index tree is left intact -
   increment vy_range->version instead.

mejedi/tarantool,rtsisyk/tarantool,rtsisyk/tarantool,rtsisyk/tarantool,mejedi/tarantool,rtsisyk/tarantool,mejedi/tarantool,mejedi/tarantool