Update Characteristics spec template

[pseys]

There's an opportunity to streamline the way we document our characteristics within Salt component and pattern specs. It may also be a useful resource for designers outside the core team.

• Add all characteristic tokens as a component in the Salt Spec Utility file -- Designers can then drop in a component and set the props depending on the tokens they need -- Providing tokens through the Spec Utilities will ensure design specs are always up-to-date
• Create a theme switcher component that can be dropped into a page to control theme variables when in prototype mode in Figma -- This removes the need for displaying dark mode examples within the characteristic spec.

[origami-z]

Minor point - "always up to date" may be a false positive one, specs need design attention whether to update from library in each file. May increase maintenance for additional component with little return

Having dark vars in spec is a good reference point. With variable modes, it should be easy to copy the whole tokens layers from top and set to dark mode at the bottom.

Maybe something in the middle ground, have a template with text set to content variable. Each token to be manually set with text and color block?