Override role as TANK based on MT assignments

This is particularly helpful in fights like High King Maulgar,
Illidari Council or Kael'Thas where a DPS player is temporarily
made into a tank.

src/types/unitframe.lua

@@ -541,10 +541,20 @@ function UnitFrame:UNIT_POWER_UPDATE()
     self:UpdatePower()
 end
 
-function UnitFrame:UpdateRole(role)
+function UnitFrame:GetRole(role)
     if role == nil then
         role = UnitGroupRolesAssigned(self.unit)
     end
+
+    if GetPartyAssignment("MAINTANK", self.unit) then
+        role = "TANK"
+    end
+
+    return role
+end
+
+function UnitFrame:UpdateRole(role)
+    role = self:GetRole(role)
     if role == "HEALER" then
         self:EnablePower(Enum.PowerType.Mana)
     elseif role == "TANK" and select(3, UnitClass(self.unit)) == 6 then

src/types/unitgroup.lua

@@ -53,8 +53,8 @@ local function UnitFrameDefaultCompare(lhs, rhs)
         end
 
         -- tank < healer < damage < ?
-        local lrole = RoleValue(UnitGroupRolesAssigned(lunit))
-        local rrole = RoleValue(UnitGroupRolesAssigned(runit))
+        local lrole = RoleValue(lhs:GetRole())
+        local rrole = RoleValue(rhs:GetRole())
 
         if lrole ~= rrole then
             return lrole < rrole