The status variable Innodb_buffer_pool_read_requests is not updated correctly

In MDEV-26827, some monitoring was changed.
Some status variables were changed to point directly to the underlying variables, like this:

  {"buffer_pool_read_requests", &buf_pool.stat.n_page_gets, SHOW_SIZE_T},

Unlike all other variables in buf_pool.stat this particular one is divided into shards for performance reasons (MDEV-21212). So, the status variable would only reflect the contents of the first shard and not the entire counter. Thanks to dragle for noticing this.

Note: This counter is inaccurate by design. If we protected it correctly, it would introduce a performance bottleneck.