Implement support for icons.

[pixlwave]

This PR makes the following changes:

• Adds a CompoundIcon component that works similarly to Image(systemName:) whereby it reads the current font size and scales with it appropriately.
• Adds a CompoundIcons struct that contains a manual mapping of all the tokens so we can use them via a KeyPath as the style dictionary is currently fixed to generate static properties (PR to fix this is here).
• Adds a dynamic type setting to the inspector when used on a Mac and adopts SwiftUI's new value based navigation so this is only applied to the detail view's contents.
• Updates to the latest revision of the tokens repo.