Core/Spells: Replace MovePosition by MovePositionToFirstCollision in spell dest target handling.

- Solves issues such as being able to summon creatures inside terrain/gameobjects, being able to fall through terrain by using Shadowstep/Feral Charge (Cat), and much more
Merge pull request #12021 from Trisjdc/spell_target_dest

Core/Spells: Replace MovePosition by MovePositionToFirstCollision in spell dest target handling.