* Add *mobattached and *killmonstergid script command

[AnnieRuru]

Pull Request Prelude

• I have followed proper Hercules code styling.
• I have read and understood the contribution guidelines before making this PR.
• I am aware that this PR will be closed if the above-mentioned criteria are not fulfilled.

Issues addressed

Actually I was writing this for my custom scripts,
but when I do a search OnTouchNPC in npc folder, suddenly found this is actually official

rAthena already having *getattachedrid like for ages already
https://github.com/rathena/rathena/blob/master/doc/script_commands.txt#L922-L925

Changes Proposed

Add *mobattached and *killmonstergid script command

Tested with

prontera,155,185,5	script	qwer	1_F_MARIA,{
	getmapxy .@map$, .@x, .@y, UNITTYPE_NPC;
	.@mobid = monster( .@map$, .@x, .@y, "--ja--", PORING, 1, strnpcinfo(0)+"::Onaaa" );
	unitwalk .@mobid, 160,185;
	end;
Onaaa:
	npctalk "run";
	end;
}
prontera,160,185,5	script	asdf	1_F_MARIA,0,0,{
	end;
OnTouchNPC:
//	unitkill mobattached();
	killmonstergid mobattached();
//	unitemote mobattached(), e_gg;
	end;
}

Affected Branches

• Master

Known Issues and TODO List

I accidentally push this branch into main hercules repo, need to remove it

[HerculesWSAPI]

This change is