Bug fixes, init signals for mobs, density updates. (#21108)

1. Look up now follows your mob (no more auto-removal when you move,
only when you go below a solid tile). Maybe add a hotkey?
2. Made the codebase work with the latest version of spacemandmm lint.
3. Advanced kits don't work on robotic limbs.
4. Density shifting should now always use set_density. Ported
TRAIT_UNDENSE from CM to better control the density of living mobs.
Fixes weird shifting behaviour with wall leaning -- what was happening
is that mob density was getting reset to TRUE because the mob wasn't
lying down.
5. TGUI say light prefs actually save.

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Co-authored-by: Matt Atlas <liermattia@gmail.com>

code/modules/modular_computers/file_system/programs/security/camera.dm

@@ -150,7 +150,7 @@
 		return FALSE
 
 	set_current(C)
-	user.machine = ui_host()
+	user.set_machine(ui_host())
 	user.reset_view(current_camera)
 	check_eye(user)