There's no specialization with that name in the game. However, you might be thinking of a different specialization:
* "Arcane Warrior": This specialization is available to warriors and focuses on combining magic and combat. It's acquired through the "The Urn of Sacred Ashes" quest, which you can access after completing the "The Landsmeet" quest.
It's possible there's a mod that introduces a "Spellweaver" specialization, but it's not a part of the vanilla game.