This adds the server property `Paper.DisableClassPrioritization` to disable
prioritization of own classes for plugins' classloaders.
This value is by default not present, and this will therefore break any
plugins which abuse behaviour related to not using their own classes
while still loading their own. This is often an issue with failing to
relocate or shade properly, such as when shading plugin APIs like Vault.
A plugin's classloader will first look in the same jar as it is loading
in for a requested class, then load it. It does not re-use other
plugins' classes if it has the chance to avoid doing so.
If a class is not found in the same jar as it is loading for and it does
find it elsewhere, it will still choose the class elsewhere. This is
intended behaviour, as it will only prioritise classes it has in its own
jar, no other plugins' classes will be prioritised in any other order
than the one they were registered in.
The patch in general terms just loads the class in the plugin's jar
before it starts looking elsewhere for it.
