Thour tiny tutorial tweaks (and a unit test)

[SabreML]

About the pull request

1. Commit 5014927: Makes the 'Tutorial Menu' automatically close when a tutorial is started.
   • Also adds an abort_tutorial() call to /datum/tutorial/proc/start_tutorial(), since it may have been possible to for player to get trapped in the tutorial otherwise.
2. Commit b10974c: Adds a tutorial_id to the basic Xenomorph tutorial.
3. Commit 38c03c9: Edited the tutorial Xenomorph a bit so that it's always "You are Inquisitive Drone (XX-123)", as opposed to "You are Inquisitive Young/Mature/etc. Drone (XX-123)".
4. Commits a595b97 + 27e38e6: Adds a basic unit test for /datum/tutorial subtypes to verify that they have set some basic variables.
   • Also lightly organises the #includes in code/modules/unit_tests/_unit_tests.dm.

Explain why it's good for the game

Just a couple of things I noticed while exploring tutorial code.
The third commit is maybe a bit subjective, but I personally think it makes the tutorials seem like more of a separate game state, if that makes sense.

Testing Photographs and Procedure

Screenshots & Videos

Put screenshots and videos here with an empty line between the screenshots and the <details> tags.

Changelog

🆑
ui: Made the Tutorial Menu automatically close when a tutorial is started.
code: Made the tutorial Xenomorph not inherit the user's 'age' prefix.
code: Added a basic unit test for tutorials.
/:cl:

[SabreML]

Missed a 'T' opportunity.

[harryob]

well that's depressing

[Zonespace27]

Thank you for the unit test!