Migrate to Adventure API

[SmylerMC]

Why migrate

Mojang and paper are phasing out legacy text formatting codes and text composition APIs (Bungee chat, Bukkit ChatColor, etc), in favor of Adventure API.

TerraPlusMinus uses legacy inline formatting codes and deprecated APIs in many places. We should aim to proactively migrate to Adventure API before those legacy interfaces are definitively removed.

The migration should be quite straightforward and mostly transparent to end users, except maybe for the prefix plugin configuration option.

Proposed approach for the prefix configuration option:

1. migrate prefix over to Adventure's legacy serializer
2. add a chatPrefix option taking a serialized text component, and fall back to it when prefix is unset
3. log a warning when the plugin is loaded to encourage users to migrate from prefix to chatPrefix

Useful resources:

• Adventure API documentation
• Adventure API migration guide
• Adventure Javadoc