`AutoWorld.World`s can set required_server_version and required_client_version properties. Drop `get_required_client_version()`.
`MultiServer` will set an absolute minimum client version based on its capability (protocol level).
`IgnoreVersion` tag is replaced by using `Tracker` or `TextOnly` with empty or null `game`.
Ignoring game will also ignore game's required_client_version (and fall back to server capability).
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