Hitby refactor (#19624)

Refactored hitby to be in line with TG's version.
Refactored item weight defines to a more clear naming scheme, also in
line with TG's version.
Refactored how the movement bumps are handled, ported signals to handle
them, in preparation for the movement update.
Fixed disposal hit bouncing the hitting atom on the wall.
Items do not push other items anymore if they are tiny.

code/modules/modular_computers/computers/subtypes/dev_handheld.dm

@@ -12,7 +12,7 @@
 	can_reset = TRUE
 	hardware_flag = PROGRAM_TABLET
 	max_hardware_size = 1
-	w_class = ITEMSIZE_SMALL
+	w_class = WEIGHT_CLASS_SMALL
 	looping_sound = FALSE
 
 /obj/item/modular_computer/handheld/Initialize()

code/modules/modular_computers/computers/subtypes/dev_silicon.dm

@@ -10,7 +10,7 @@
 	base_active_power_usage = 25
 	max_hardware_size = 3
 	max_damage = 50
-	w_class = ITEMSIZE_NORMAL
+	w_class = WEIGHT_CLASS_NORMAL
 	enrolled = DEVICE_PRIVATE
 	/// Thing that contains this computer. Used for silicon computers
 	var/mob/living/silicon/computer_host

code/modules/modular_computers/computers/subtypes/dev_telescreen.dm

@@ -15,7 +15,7 @@
 	max_hardware_size = 2
 	steel_sheet_cost = 10
 	light_range = 4
-	w_class = ITEMSIZE_HUGE
+	w_class = WEIGHT_CLASS_HUGE
 	is_holographic = TRUE
 
 /obj/item/modular_computer/telescreen/attackby(obj/item/attacking_item, mob/user)