Support for design tokens from C#

[vnbaaij]

As suggested/requested in issue #114, we want a way to programmatically work with design tokens. We are addressing this in PR #142 and are almost at a point where we are merging that in. You can look at a working situation at https://brave-cliff-0c0c93310-142.centralus.azurestaticapps.net/. The Theme switch and the 'Web components handlers' button are styled with the BaseLayerLuminance design token. The other buttons use the BaseHeightMultiplier token.

We are looking for need some confirmation form the community on if our direction would be considered the best solution for this.

The way we have implemented this now is that every design token (about 160 in total) is as an implementation of the generic DesignToken class. This means you would get a BaseFont class, a BaseLayerLuminance class, etc. . The classes are created with a source generator and added to the DI container in the AddFluentUIComponents extension (as transient dependencies) with an (also source generated) extension AddDesignTokens(). This means the design tokens can then by injected and used when needed. Besides being injected, every design token can also be used as a component (to wrap some other components where the design token needs to be applied). Of course there are other pro's and con's to this approach:
Pro

• Inject just what is needed
• Tiny classes tailored to a specific goal that are source generated so they don't clutter the code
• Every design token can also be used as a component (to wrap some other components where the design token needs to be applied)

Con

• Lot of classes added to the DI container

An alternative approach would be to keep using the generic DesignToken<> type (a design token can have a string or int or float value) and have a class with const values (DesignTokenNames) for all the standard design token names and a DesignTokens class that contains properties for all these standard design tokens. The DesignTokens class is added to the DI container, so you can inject it whenever it is needed. This has some pro's and con's:
Pro

• Discoverability is pretty easy once you have injected the DesignTokens

Con

• All design tokens are being created and initialized even if you only need one
• Initialization takes a lot of repeated code when newing up the properties

Please take a look at the code as how it is int the PR (#142) at the moment, consider how it would change when the alternative would be implemented and let us know what you think the best solution would look like.