Medical/roller beds (#78078)

## About The Pull Request

'medical beds' in the game were just varedited survival pod beds. This
creates a proper medical bed subtype plus its own sprite for regular and
roller beds. Cleans up little bits of the bed code and adds context
helpers.

- Medical/roller bed is now constructable with titanium and plastic
after research
- Bed will face the correct direction when pulled
- Movable beds can have 'brakes' toggled with alt-click


![medical_bed_1](https://github.com/tgstation/tgstation/assets/83487515/dd197e24-cf72-4240-ac5a-8cdf575eca00)


![para_bed_1](https://github.com/tgstation/tgstation/assets/83487515/8ad5103e-57be-4dca-8a32-33bdabbeb82e)

## Why It's Good For The Game

Medical gets their own bed, new sprites, cleans up varedits on maps.

## Changelog

🆑 LT3
image: New medical bed and emergency roller bed
code: Added context hints for beds
/🆑

---------

Co-authored-by: Time-Green <7501474+Time-Green@users.noreply.github.com>

code/game/objects/effects/spawners/random/medical.dm

@@ -132,7 +132,7 @@
 	name = "patient stretcher spawner"
 	icon_state = "rollerbed"
 	loot = list(
-		/obj/structure/bed/roller,
+		/obj/structure/bed/medical/emergency,
 		/obj/vehicle/ridden/wheelchair,
 	)