Rimewoad Sorcerer Updated

Based on feedback and review, this subclass for sorcerer has been updated. New 18th-level feature and some clerification edits, plus swapped armor of Agathys for fog cloud, and altered Frost Touched Magic to follow the style introduced in Tasha’s Cauldron of Everything (side note, I will be offering optional rules for pre-TCoE sorcerers to get the same spells known expansion feature since it seems to resonate with players and DMs).