"default collation" ids for the protocol

Connection protocol only has one byte for selecting a collation. This is no longer enough. So connectors are forced to do SET NAMES on every connection.

On the other hand, normally connectors don't care about a collation and only need to set a correct character set, and that most of the time is utf8.

There are 41 unused values in the 0-255 range of collation ids.
They could be used for "default collation" ids, like, for example, "220 = default collation of utf8mb4", etc.

Then a connector will still be able to use one-byte in the protocol to set a character set of its choice and won't need SET NAMES.