Add MapX support

[kamronbatman]

Add MapX support against CharacterListFlags.CLF_UNLOCK_FELUCCA_AREAS flag received from server.
cc @MaxKellermann on the best way to do this.

Mul files:
$"map{i}x.mul"
$"statics{i}x.mul"
$"staidx{i}x.mul"

UOP:
File: $"map{i}xLegacyMUL.uop"
Entry: $"build/map{i}legacymul/{{0:D8}}.dat"

Note: ClassicUO has since removed multi-threaded loading of client files. Was this even a good move or necessary?

Also Note, ClassicUO has an issue where two sources access the map at the same time:
ClassicUO/ClassicUO@a01096b

[MaxKellermann]

What is MapX?

[kamronbatman]

Apparently an alternate set of maps that has extra areas which are unlocked when the client flags are sent. Probably related to subscriptions/expansions.

On the EA client, the map/statics are not streamed in until you actually enter Britannia. This means which set of files are used can be determined once at the appropriate time. I believe by default ClassicUO loads everything at bootstrap.