Add option to show true LastArea in FileSelect

[ErynGalen]

This adds an Everest option to show the SID of unavailable maps in the FileSelect menu, instead of showing the vanilla progression.

[ErynGalen]

Example:

[maddie480]

The "discussion" the 6-month-old label refers to is "should this really be an option? or should it just be... implemented without a switch?" I don't remember if the discussion really happened

[maddie480]

:despaireline: the discussion never happened

[microlith57]

i feel like there is no reason we wouldn't want this behaviour, it's kinda just obviously correct. is there a reason anyone would want to have this option turned off?

[DashingCat]

I agree with @microlith57, I believe this does not need to be an option.

However, the current implementation conflicts with the mod CollabUtils2.

The IL manipulation in this PR removes the reference to the field Celeste.AreaData.Name, which is used here in modSelectSlotLevelSetDisplayName: https://github.com/EverestAPI/CelesteCollabUtils2/blob/cc0609b38505bd5a0442c3933367bd3400634576/LobbyHelper.cs#L679-L698

With the changes in the PR applied, the collab name is no longer used, and instead the last area of the collab is shown (for example, for the Strawberry Jam collab, the name shown on the file select slot is Grandmaster Lobby instead of Strawberry Jam Collab).

[SnipUndercover]

With the changes in the PR applied, the collab name is no longer used, and instead the last area of the collab is shown (for example, for the Strawberry Jam collab, the name shown on the file select slot is Grandmaster Lobby instead of Strawberry Jam Collab).

@DashingCat Should we be worried about this? The collab will be unloaded anyway, making its collab name not present in the HashSet<string> collabNames.

[SnipUndercover]

Where does the value 580 come from?

[SnipUndercover]

As seen in the conversation in the comments, the new behavior seems more correct and there doesn't seem to be a reason to keep the old one around. The setting therefore is unnecessary.