ResetConnectionAsync doesn't preserve `character_set_connection`

[bgrainger]

ResetConnectionAsync (added in ffea494 for #831) only sends a connection reset packet. This sets the connection charset to the server default charset, not the initial connection charset: https://bugs.mysql.com/bug.php?id=97633

Consequently, result sets may have the wrong encoding for commands subsequently executed on the connection.

We should abstract away this bug from the consumer by automatically executing SET NAMES. With pipelining (#1088) this won't be any less efficient.

[bgrainger]

automatically executing SET NAMES

Note that this is unnecessary for MariaDB: #1236. So the current behaviour is desirable for that DB backend.