Make it possible to lock trap doors and stairs

[brightrim]

It should be possible, with a minor hack using an invisible item to block the stairs, to allow trap doors and the connected stairs to be locked from either end. Implementation would have to differ between housing and outside, due to the unpredictable locations of stairs and connected trap doors outside of housing.

To do:

• [x] Allow keys to lock a trap door
• [x] When locking a trap door, find the connected stair via item datavalues if not housing, via predictable location if housing, and lock the stair as well while adding an invisible item 4339 to block it from being walked
• [x] Add custom description to stair when locked to indicate its status
• [x] Allow keys to unlock trap doors, which should also unlock the stair and remove the invisible item blocking it
• [x] Allow estates in housing to create a lock for their trap doors and/or stairs (these are paired, so making a lock for one will make it for the other at the same time)

[brightrim]

Coded but can not be pushed for testing until the problem of protected files in git has been resolved, as two of the involved files are for unknown reasons listed as protected from change and thus I am unable to put in the changes.

[brightrim]

Found a way to circumvent the issue this time and not have to edit the protected files, though really something that needs to be fixed soon for future development.

[brightrim]

Testing thread: https://discord.com/channels/401855954272124940/1211785094470307921