Fix `AreaObject` matchers

[tal5]

Reported on Discord.

Changes

• AreaContainmentObject#areaBaseAdvancedMatches now uses MatchHelper#doesMatch(String, ExactChecker), to be consistent with other object types and allow matchers like *_area|area_flagged:thing.
• AreaContainmentObject now extends FlaggableObject directly instead of extending ObjectTag and having unsafe casts to FlaggableObject.
• As AreaContainmentObject is a FlaggableObject, it now uses AbstractFlagTracker#registerFlagHandlers in it's register method instead of every impl having to specify that seperatley
• AreaObject.players now uses the ListTag filter convertor constructor, and now uses the PlayerTag constructor directly instead of mirrorBukkitPlayer (as the player's are definitely not null).
• AreaObject.living_entities now uses the ListTag filter convertor constructor.
• AreaObject.is_within now uses instanceof pattern matching.
• AreaObject.is_within now directly uses World#equals instead of String#equalsIgnoreCase on their names (World#equals compares the world's UUIDs).
• Removed the redundant CuboidTag boundary variable from AreaObject.approximate_overlap_areas in favor of calling area.getCuboidBoundary() in-line.
• All AreaContainmentObject implementations now just extend AreaContainmentObject instead of separately extending ObjectTag and FlaggableObject - let me know if that was there just for clarity and should be reverted, but imo it's pretty clear with AreaContainmentObject's naming & being able to just hover over it and all.

[!NOTE] Might be a good idea to add a EntityTag#mirrorBukkitEntity style method that automatically calls #getDenizenObject? that way entity -> new EntityTag(entity).getDenizenObject() could be EntityTag::mirrorBukkitEntity and be a little cleaner.

[mcmonkey4eva]

Might be a good idea to add a EntityTag#mirrorBukkitEntity style method that automatically calls #getDenizenObject? that way entity -> new EntityTag(entity).getDenizenObject() could be EntityTag::mirrorBukkitEntity and be a little cleaner. yeah that'd be good to have

[tal5]

Might be a good idea to add a EntityTag#mirrorBukkitEntity style method that automatically calls #getDenizenObject? that way entity -> new EntityTag(entity).getDenizenObject() could be EntityTag::mirrorBukkitEntity and be a little cleaner. yeah that'd be good to have

Added EntityTag#mirrorBukkitEntity.