Converts Reagents to Typepaths and Centralises Reagent Spawning (#9140)

Converts reagents to use typepaths instead of IDs.
    Centralises reagent spawning in a lot of places to use reagents_to_add instead of a variety of custom methods or initialise overrides.

code/modules/spell_system/artifacts/items/lich_phylactery.dm

@@ -15,7 +15,7 @@
 	. = ..()
 	world_phylactery += src
 	create_reagents(120)
-	reagents.add_reagent("undead_ichor", 120)
+	reagents.add_reagent(/datum/reagent/toxin/undead, 120)
 
 /obj/item/phylactery/Destroy()
 	to_chat(lich, "<span class='danger'>Your phylactery was destroyed, your soul is cast into the abyss as your immortality vanishes away!</span>")

code/modules/spell_system/spells/spell_list/others/generic/entangle.dm

@@ -28,7 +28,7 @@
 	seed.name = "heirlooms"
 	seed.seed_name = "heirloom"
 	seed.display_name = "vines"
-	seed.chems = list("nutriment" = list(1,20))
+	seed.chems = list(/datum/reagent/nutriment = list(1,20))
 
 /spell/targeted/entangle/cast(var/list/targets)
 	for(var/mob/M in targets)

code/modules/spell_system/spells/spell_list/self/conjure/plant_sanctuary.dm

@@ -27,7 +27,7 @@
 	name = "merlin tears"
 	seed_name = "merlin tears"
 	display_name = "merlin tears"
-	chems = list("bicaridine" = list(3,7), "dermaline" = list(3,7), "dylovene" = list(3,7), "tricordrazine" = list(3,7), "alkysine" = list(1,2), "imidazoline" = list(1,2), "peridaxon" = list(4,5))
+	chems = list(/datum/reagent/bicaridine = list(3,7), /datum/reagent/dermaline = list(3,7), /datum/reagent/dylovene = list(3,7), /datum/reagent/tricordrazine = list(3,7), /datum/reagent/alkysine = list(1,2), /datum/reagent/imidazoline = list(1,2), /datum/reagent/peridaxon = list(4,5))
 	kitchen_tag = "berries"
 
 /datum/seed/merlin_tear/setup_traits()