[Spells] Implemented SPA 463 SE_SHIELD_TARGET (#4224)

SPA 463 SE_SHIELD_TARGET

Live description: "Shields your target, taking a percentage of their damage".

Only example spell on live is an NPC who uses it during a raid event "Laurion's Song" expansion. SPA 54492 'Guardian Stance' Described as 100% Melee Shielding

Example of mechanic. Base value = 70. Caster puts buff on target. Each melee hit Buff Target takes 70% less damage, Buff Caster receives 30% of the melee damage.
Added mechanic to cause buff to fade if target or caster are separated by a distance greater than the casting range of the spell. This allows similar mechanics to the /shield ability, without a range removal mechanic it would be too easy to abuse if put on a player spell. *can not confirm live does this currently

Can not be cast on self.

zone/spells.cpp

@@ -863,6 +863,14 @@ bool Mob::DoCastingChecksOnTarget(bool check_on_casting, int32 spell_id, Mob *sp
 			}
 		}
 	}
+	/*
+		Cannot cast shield target on self
+	*/
+	if (this == spell_target && IsEffectInSpell(spell_id, SE_Shield_Target)) {
+		LogSpells("You cannot shield yourself");
+		Message(Chat::SpellFailure, "You cannot shield yourself.");
+		return false;
+	}
 	/*
 		Cannot cast life tap on self
 	*/