Token Lab: gradients

[drwpow]

⚠ Depends on #331

Description

Allow adding/editing of gradient tokens in Token Lab.

Figma Design

Definition of done

• Gradient tokens can be added/edited/removed
• All alias-able subparts of the token are supported, from color aliasing to color tokens, to position aliasing to number tokens
• There is SOME sort of visualiztion showing the gradient, but no requirements on what that visualization looks like so long as it exists, and reflects the current values.