integrate ex-n-ui-foundations styles into dotcom-ui-base-styles

[apaleslimghost]

updates the n-ui-foundations styles included in #1062 to fit more into the Page Kit ecosystem, with an O3 future in mind. notably, this removes support for using dotcom-ui-base-styles in components, and recommends that components use Origami styles directly (there is no longer a need to have a default bundled set of styles for both components and apps, this is handled via peerDependencies).

this PR starts consuming o3-foundation as a dependency, to replace nUiZIndexFor with o3-foundation's z-index variables. there's no way to import just the z-index variables, so this imports the whole of o3-foundation. until we migrate dotcom-ui-base-styles fully to o3, this will increase the CSS bundle size. that's a tradeoff i'm willing to make for the next few months, to facilitate an easier migration path.