Internalize @microsoft/fast-components

[fcollonval]

This PR internalizes the code from the deprecated package @microsoft/fast-components.

It also:

• Update the color recipe to use an accentColor and a neutralColor design token easing the change of the theme
• Adds the components: design-system-provider, disclosure, picker and skeleton.

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Fixes #79

[github-actions]

👈 Launch a Binder on branch jupyterlab-contrib/jupyter-ui-toolkit/maintenance/internalize-fast-components

[jtpio]

Is that change temporary, so the warning reported in #79 does not show up in the yarn logs anymore?

If so, is there a long-term plan that would not require to vendor @microsoft/fast-components in this repo?

[fcollonval]

It is not temporary - it is definitive change.

[jtpio]

If so, is there a long-term plan that would not require to vendor @microsoft/fast-components in this repo?

And for this question?

Asking to get a better idea of the implications, and what that would mean in terms of maintenance work for maintainers in case this proposal is accepted: jupyterlab/frontends-team-compass#227