Resource packs (Add sending resource packs)

[theaddonn]

The logic behind sending resource packs (not via CDNs) is not implemented yet.

[theaddonn]

The general login sequence implementation is aimed to be moved out of the bedrockrs_proto crate and into the bedrock-server crate. See issue #56.
But this is still needed since the logic behind sending direct packs is planned to be in bedrockrs_proto