fix(WG): FFA quest credit for crossfaction WG kills

[Nyeriah]

Summary

When a player is flipped to the opposite team by CFBG in Wintergrasp, the WG PvP-kill quests (Slay Them All 13180/13178 for Horde, No Mercy for the Merciless 13179/13177 for Alliance) didn't advance.

A real-Horde player flipped to Alliance still holds the Horde quest (needs credit NPC 31086), but the existing hook only granted one credit NPC chosen by the killer's assigned team — so killing Horde as flipped-Alliance gave 39019 (Alliance-side credit) and the original quest stayed at 0.

Fix

OnBattlefieldPlayerKill now iterates both teams' war players within 40y of the killer and grants both PvP-kill credit NPCs to each. Granting credit for a quest the player doesn't hold is a no-op, so this is safe for non-flipped players.

The core's lieutenant-victim path (BattlefieldWG.cpp) still grants one credit ID to killer-team players. To avoid double-credit on that specific quest tick, the hook skips the core-side credit for killer-team players when the victim has SPELL_LIEUTENANT (55629).

Credit matrix per kill

Victim	Player team vs killer	coreCredit	otherCredit
Lieutenant	Killer's team	core gives	hook gives
Lieutenant	Opposite team	hook gives	hook gives
Non-lieutenant	Killer's team	hook gives	hook gives
Non-lieutenant	Opposite team	hook gives	hook gives

Every war player in range gets both credit IDs exactly once per kill, regardless of faction flips.

Test plan

• Real-Horde player with Slay Them All (13180) gets flipped to Alliance, kills a Horde player → kill counter advances.
• Real-Alliance player with No Mercy for the Merciless (13179) gets flipped to Horde, kills an Alliance player → kill counter advances.
• Non-flipped players continue to advance their own quests normally.
• Lieutenant kills do not grant double credit on a single quest.

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