Fix a couple of bugs in the Designer plugin

[bheston]

Pull Request

Description

Fix two bugs:

• Support for "transparent" as a constant color value
• Tokens getting applied for the correct intended style properties

Test Plan

Tested in Figma plugin.

Checklist

General

• I have included a change request file using $ npm run change
• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation for this project.