[B+C] Add player unique ID to (Async)PlayerPreLoginEvent. Adds BUKKIT-5108

[B+C] Add player unique ID to AsyncPlayerPreLoginEvent. Adds BUKKIT-5108

The Issue:
Mojang is slowly migrating the identification of players from their name to their unique ID. For plugins it could be useful to have this UniqueID in a very early state of the connection process.

Justification for this PR:
AsyncPlayerPreLoginEvent is called in a very early state of the connection process. So it would be best to add the UniqueID to AsyncPlayerPreLoginEvent.
For instance a ban plugin could use the UniqueID to be aware of the future possibility to change user names.

PR Breakdown:
Added a new field and getter method for UniqueID. Also deprecated the old constructor and created a new one with the additional parameter.

Testing Results and Materials:
See CB PR

Relevant PR:
CB-1289 - https://github.com/Bukkit/CraftBukkit/pull/1289

JIRA Ticket:
BUKKIT-5108 - https://bukkit.atlassian.net/browse/BUKKIT-5108