Lua API: Add register_on_chatcommand to SSM and CSM (#7862)

Allows catching a chatcommand call just after the command and the
parameters are parsed but before its existence is checked and before the
corresponding function is run. Returning `true` from a callback function
will prevent default handling of the command leaving mods to handle the
command manually.

builtin/client/chatcommands.lua

@@ -23,6 +23,11 @@ core.register_on_sending_chat_message(function(message)
 		return true
 	end
 
+	-- Run core.registered_on_chatcommand callbacks.
+	if core.run_callbacks(core.registered_on_chatcommand, 5, cmd, param) then
+		return true
+	end
+
 	local cmd_def = core.registered_chatcommands[cmd]
 	if cmd_def then
 		core.set_last_run_mod(cmd_def.mod_origin)

builtin/client/register.lua

@@ -63,6 +63,7 @@ core.registered_on_mods_loaded, core.register_on_mods_loaded = make_registration
 core.registered_on_shutdown, core.register_on_shutdown = make_registration()
 core.registered_on_receiving_chat_message, core.register_on_receiving_chat_message = make_registration()
 core.registered_on_sending_chat_message, core.register_on_sending_chat_message = make_registration()
+core.registered_on_chatcommand, core.register_on_chatcommand = make_registration()
 core.registered_on_death, core.register_on_death = make_registration()
 core.registered_on_hp_modification, core.register_on_hp_modification = make_registration()
 core.registered_on_damage_taken, core.register_on_damage_taken = make_registration()

builtin/game/chat.lua

@@ -58,6 +58,11 @@ core.register_on_chat_message(function(name, message)
 
 	param = param or ""
 
+	-- Run core.registered_on_chatcommands callbacks.
+	if core.run_callbacks(core.registered_on_chatcommands, 5, name, cmd, param) then
+		return true
+	end
+
 	local cmd_def = core.registered_chatcommands[cmd]
 	if not cmd_def then
 		core.chat_send_player(name, "-!- Invalid command: " .. cmd)

builtin/game/register.lua

@@ -584,6 +584,7 @@ core.unregister_biome = make_wrap_deregistration(core.register_biome,
 		core.clear_registered_biomes, core.registered_biomes)
 
 core.registered_on_chat_messages, core.register_on_chat_message = make_registration()
+core.registered_on_chatcommands, core.register_on_chatcommand = make_registration()
 core.registered_globalsteps, core.register_globalstep = make_registration()
 core.registered_playerevents, core.register_playerevent = make_registration()
 core.registered_on_mods_loaded, core.register_on_mods_loaded = make_registration()