fix(Scripts/Creature): multi-raid faction leader credit

[avarishd]

Changes Proposed:

This PR proposes changes to:

• Core (units, players, creatures, game systems).
• Scripts (bosses, spell scripts, creature scripts).
• Database (SAI, creatures, etc).

Give credit to all players from the opposing faction, in the same area, when a faction leader is slain.
Moved Velen & Magni from SAI

Issues Addressed:

• Closes Players not getting credit for multi-raid faction leader kills #12243

SOURCE:

The changes have been validated through:

• Live research (checked on live servers, e.g Classic WotLK, Retail, etc.)
• Sniffs (remember to share them with the open source community!)
• Video evidence, knowledge databases or other public sources (e.g forums, Wowhead, etc.)
• The changes promoted by this pull request come partially or entirely from another project (cherry-pick). Cherry-picks must be committed using the proper --author tag in order to be accepted, thus crediting the original authors, unless otherwise unable to be found

more info in the issue

Tests Performed:

This PR has been:

• Tested in-game by the author.
• Tested in-game by other community members/someone else other than the author/has been live on production servers.
• This pull request requires further testing and may have edge cases to be tested.

How to Test the Changes:

• This pull request can be tested by following the reproduction steps provided in the linked issue
• This pull request requires further testing. Provide steps to test your changes. If it requires any specific setup e.g multiple players please specify it as well.

as horde (char1)
.go c id 29611/7999/2784/17468
(char 2)
.tele stormw/darn/ironforge/exo

as alliance (char1)
.go c id 3057/4949/10181/16802
(char 2)
.tele thunder/orgri/undercity/silvermoon

Known Issues and TODO List:

• [ ]
• [ ]

How to Test AzerothCore PRs

When a PR is ready to be tested, it will be marked as [WAITING TO BE TESTED].

You can help by testing PRs and writing your feedback here on the PR's page on GitHub. Follow the instructions here:

http://www.azerothcore.org/wiki/How-to-test-a-PR

REMEMBER: when testing a PR that changes something generic (i.e. a part of code that handles more than one specific thing), the tester should not only check that the PR does its job (e.g. fixing spell XXX) but especially check that the PR does not cause any regression (i.e. introducing new bugs).

For example: if a PR fixes spell X by changing a part of code that handles spells X, Y, and Z, we should not only test X, but we should test Y and Z as well.