Add PlayerDamageByPlayerEvent

[srnyx]

Description

Added the PlayerDamageByPlayerEvent event which will trigger when a player attacks another player (PVP). This event extends EntityDamageByEntityEvent

Motivation and Context

This is a simple feature that just makes it easier to listen to PVP.

How Has This Been Tested?

Tested by using another plugin and adding the PlayerDamageByPlayerEvent event handler. It works as intended.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have read the CONTRIBUTING document.
• All new and existing tests passed.