Core/Threat: Send SMSG_HIGHEST_THREAT_UPDATE when a reference returns online - #32012

Changes proposed:

• Send SMSG_HIGHEST_THREAT_UPDATE when a reference returns online
• This applies to cases where the player is offline in another phase; upon return online reference, the packet must be sent again to show that player the threat of that NPC.
• This is necessary for encounters with bosses like Halion, one player enters in twilight realm and attacks Twilight Halion, while the other players appear on Twilight Halion's threat list as offline ref. When another player enters in twilight realm and attack Twilight Halion, they cannot see the threat (whether in the tooltip, under Settings > Interface > Display > Show Aggro Percentages, or in addons like Omen) until the boss switches targets and resends the data packet to online players refs.

retail Proofs:

• https://youtu.be/8M8rSy7K3Rc?t=85
• https://youtu.be/FcCdGtp--kw?t=89
• https://youtu.be/a3ANZ1rcR5M?t=119

Issues addressed:

None

Tests performed:

Tested in the Halion encounter with 3 players (2 tanks, 1 DPS).

Before the fix:

• Tank 1 enters the twilight realm and attacks Twilight Halion.
• Tank 2 and the DPS wait ~2 seconds, then enter the twilight realm.
• Tank 2 and the DPS attack Halion but do not see their threat % or the threat list at all.
• Tank 2 taunts Halion to force a target change, only then does the threat list/percentage appear.

After the fix:

• Same steps repeated. Tank 2 and the DPS see their threat % and the threat list correctly as soon as they start attacking, with no taunt required.