Core/Movement: allow focused spells to not break movement if it's movement allowed spell

Port From (https://github.com/TrinityCore/TrinityCore/commit/9ef39fa5d2f76459e3e529a0877655b0f69b98d6)

Source/Game/Entities/Creature/Creature.cs

@@ -2780,7 +2780,7 @@ namespace Game.Entities
                 AddUnitState(UnitState.CannotTurn);
         }
 
-        public bool IsFocusing(Spell focusSpell = null, bool withDelay = false)
+        public override bool IsFocusing(Spell focusSpell = null, bool withDelay = false)
         {
             if (!IsAlive()) // dead creatures cannot focus
             {

Source/Game/Entities/Unit/Unit.Spells.cs

@@ -30,7 +30,10 @@ namespace Game.Entities
     {
         public virtual bool HasSpell(uint spellId) { return false; }
 
-
+        public virtual bool IsFocusing(Spell focusSpell = null, bool withDelay = false)
+        {
+            return false;
+        }
 
         // function uses real base points (typically value - 1)
         public int CalculateSpellDamage(Unit target, SpellInfo spellProto, uint effect_index, int? basePoints = null, uint castItemId = 0, int itemLevel = -1)
@@ -1395,6 +1398,9 @@ namespace Game.Entities
                     if (spell.GetSpellInfo().IsMoveAllowedChannel())
                         return false;
 
+            if (IsFocusing(null, true))
+                return false;
+
             // prohibit movement for all other spell casts
             return true;
         }