ExperienceOrb: no possibility of interfering in search for target entity

[ColinHDev]

Description

Currently, you have the possibility by listening for PlayerExperienceChangeEvent, stop a player, or human entity to be more specific, from receiving experience.
But by the way the experience orb entity searches for its target, there is no way for plugin developers to interfere and for example, block experience orbs to be attracted to certain players / human entities, apart from extending the whole ExperienceOrb class and overwriting the ExperienceOrb::entityBaseTick() method.
https://github.com/pmmp/PocketMine-MP/blob/master/src/entity/object/ExperienceOrb.php#L179#L175

Justification

There is a variety of situations, where you wouldn't want experience orbs being attracted to specific entities, for example:

• Human entities are an easy way to create non-player entities with player skins, for example in the Slapper plugin or player skull plugins (e.g.: https://github.com/ColinHDev/CSkull/blob/main/src/ColinHDev/CSkull/entities/SkullEntity.php#L21). In these usages, you would not want experience orbs to be attracted to your entities and rather ignore them entirely.
• When writing a plugin that allows your staff members to go completely invisible, without them going into spectator mode and pretending they left the server, you would not want experience orbs flying to your hidden staff members, which would expose them.

Possible solutions

• One suggestion was a Human::canPickupExperience() method which could be overwritten by plugins in their entity classes. But this suggestion has two flaws in my opinion: First, the method could be misleading with ExperienceManager::canPickupXp() and second, this would work for those kinds of plugins listed in the first example. But for that method to be useful for plugins listed in the second example, they would need to overwrite the Player class, which is also rather impractical, even more than overwriting the ExperienceOrb class. (The second point can be ruled out if such a method would be implemented with a class attribute, a setter and getter like Entity::hasGravity() and Entity::setHasGravity().)
• Another suggestion was an ExperienceOrbAttractEvent, which could be called before the following line https://github.com/pmmp/PocketMine-MP/blob/master/src/entity/object/ExperienceOrb.php#L178. This event would be very useful for both given plugin examples, as they could just cancel the event or maybe also provide a replacement entity with an inbuilt ExperienceOrbAttractEvent::setEntity() method, so that these plugins could not only remove experience orbs from being attracted to their entities but also give plugin developers a way to implement their own system of searching.

Alternative methods

• It should be possible to create your own ExperienceOrb class which overwrites the ExperienceOrb::entityBaseTick() method so that you would be able to make a custom search, but that approach is rather impractical.
• In the case of the first example, it would also be possible for plugins to make their entities an instance of Living or only Entity but not Human because experience orbs only search for human entities. But this is also rather impractical because you would end up just copying many methods like skin and inventory handling from the Human to your own class.