this makes PermissionAttachment more and more like Permission, except that it doesn't have a name.
Right now, the only value of this API change is that it allows breaking references to dead Permissibles, but in the future it should be possible to reuse a single PermissionAttachment on multiple Permissibles.
there is no longer such a thing as a permission granted to 'everyone', since we're no longer limited to true/false/op/notop, and regular players are now assigned the pocketmine.group.user permission.
It's possible we might want to add more restricted groups than 'user' in the future, in which case it would be behaviour-BC-breaking to change the default assigned permissions when creating a new PermissibleBase. Therefore, it's better to not assign any permissions at all and let the caller decide.
In addition, this solves the problem of implied permission subscriptions and leak on PermissibleBase construction - if base permissions are provided, it should be expected that the permissible will subscribe to those permissions.
this was used for 2 things:
- to notify parent permissibles on recalculate permissions (not needed anymore thanks to callbacks)
- subscription to chat broadcast permissions (now handled separately, again using callbacks)
therefore, it's no longer needed for PermissibleBase to reference its parent, meaning that we can have one less circular dependency in our lives.
since the only way to obtain PermissionAttachmentInfo via the API is from the Permissible API, it makes zero sense to ask the attachmentinfo for its permissible, since we obviously already had it to be able to get the info in the first place. Therefore, this is just another useless reference stopping Permissibles from being garbage-collected.
lack of permission calculation means that child permissions might not have been set correctly, so this might lead to users being able to access things they aren't supposed to.
for example, Player->recalculatePermissions() was not called when a player's op status changed, nor when a permission attachment altered permissions (potential secvuln for broadcasting).
