PlayerArgument and OfflinePlayerArgument javadoc should highlight performance issue and potential misuse

[XHawk87]

Description

Following this discussion on Discord

Relating to #586

PlayerArgument and OfflinePlayerArgument have a small performance impact that should be noted in the javadocs, and include a suggestion to use EntitySelectorArgument.OnePlayer instead.

They can also be potentially misused by a malicious player to cause a server to stall by spamming it repeatedly. This risk should be noted, and a suggestion to add appropriate permissions included.

Expected code

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Extra details

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