add support to send BossBars to players

[derklaro]

Describe the new feature

The current bridge player executor allows to send messages and titles to a player, but not boss bars. Therefore adding a new method to the executor to send a boss bar to a player should be a reasonable addition. The method should get implemented on the proxies, as this won't force us to run into api changes on the spigot site.

Noteably here is that BossBars have listeners which get called when certain variables change, such as the name or progress. We need to catch those changes and modify the old boss bar rather than creating a new one.

Why do you need this feature?

We should get close to implementing most methods that audience provides into the player executor class, while keeping backwards compatibility and not implementing methods which might generate a lot of traffic (for example actions bars).

Alternatives

The api user has to implement some sort of communication to implement bossbars himself.

Other

No response

Issue uniqueness

• Yes, this issue is unique. There are no similar issues.