Add investigate_deaths (#71112)

## About The Pull Request
Adds INVESTIGATE_DEATHS, an investigate category intended to better show
causes of death.


![image](https://user-images.githubusercontent.com/66640614/200142461-c17b5e51-1116-4eef-bbfb-49bc024c0953.png)


![image](https://user-images.githubusercontent.com/66640614/200147306-09bef76e-68c6-4f0a-bdf9-0211eb274e66.png)

Also makes suicide_act take a `mob/living` as an argument instead of a
`mob`, and some minor style improvements since apparently I hate
atomicity.

## Why It's Good For The Game
Inspired by a mysterious death and dusting. More logging and leads for
admins investigating deaths.

Also fixes #59028

## Changelog
🆑 Tattle
admin: added investigate deaths to shed some more light on unusual
demises, dustings, and gibbings
/🆑

Co-authored-by: tattle <article.disaster@gmail.com>

code/modules/mod/modules/modules_maint.dm

@@ -53,6 +53,7 @@
 	mod.wearer.client?.give_award(/datum/award/achievement/misc/springlock, mod.wearer)
 	mod.wearer.apply_damage(500, BRUTE, forced = TRUE, spread_damage = TRUE, sharpness = SHARP_POINTY) //boggers, bogchamp, etc
 	if(!HAS_TRAIT(mod.wearer, TRAIT_NODEATH))
+		mod.wearer.investigate_log("has been killed by [src].", INVESTIGATE_DEATHS)
 		mod.wearer.death() //just in case, for some reason, they're still alive
 	flash_color(mod.wearer, flash_color = "#FF0000", flash_time = 10 SECONDS)
 
@@ -329,6 +330,7 @@
 	you_fucked_up = TRUE
 	playsound(src, 'sound/effects/whirthunk.ogg', 75)
 	to_chat(mod.wearer, span_userdanger("That was stupid."))
+	investigate_log("has flown off into space due to the [src].", INVESTIGATE_DEATHS)
 	mod.wearer.Stun(FLY_TIME, ignore_canstun = TRUE)
 	animate(mod.wearer, FLY_TIME, pixel_z = 256, alpha = 0)
 	QDEL_IN(mod.wearer, FLY_TIME)

code/modules/mod/modules/modules_ninja.dm

@@ -262,6 +262,7 @@
 		return
 	var/mob/living/living_user = user
 	to_chat(living_user, span_danger("<B>fATaL EERRoR</B>: 382200-*#00CODE <B>RED</B>\nUNAUTHORIZED USE DETECteD\nCoMMENCING SUB-R0UTIN3 13...\nTERMInATING U-U-USER..."))
+	living_user.investigate_log("has been gibbed by using a MODsuit equipped with [src].", INVESTIGATE_DEATHS)
 	living_user.gib()
 
 /obj/item/mod/module/dna_lock/reinforced/on_emp(datum/source, severity)