DB/Dungeons: Add instance portals for Shadowlands dungeons

[jasongdove]

Changes proposed:

• Adds cosmetic instance portals for Shadowlands dungeons
• Adds world safe locations and teleports for Shadowlands dungeons
• Adds custom areatriggers to zone in and out of Shadowlands dungeons
  • Darkmaul Citadel has no entrance areatrigger; it requires LFG
• Future work will add portals for raids

Issues addressed:

Helps with #19362

Tests performed:

Tested in-game.

Known issues and TODO list: (add/remove lines as needed)

• Torghast areatrigger was not added; there are more complex conditions required for this