[B+C] Add API to get last known player name. Add BUKKIT-5551

The Issue:

There is no api to get last known player name in case future name changing.

Justification for this PR:

This adds a simple getLastKnownName to OfflinePlayer

PR Breakdown:

Bukkit

Add getLastKnownName to OfflinePlayer

CraftBukkit

Implement getLastKnownName by getting correct nbttag

Relevant PR(s):

CB-1365 - https://github.com/Bukkit/CraftBukkit/pull/1365 - Associated CraftBukkit PR

JIRA Ticket:

BUKKIT-5551 - https://bukkit.atlassian.net/browse/BUKKIT-5551