Expose calcite-components CSS variables for spacing

[jmanke]

Description

Add CSS variables with the spacing sizes calcite-components uses. For example, --calcite-spacing-1: 0.25rem or --calcite-spacing-3: 0.75rem. This would allow consumers of calcite-components to have consistent spacing throughout their project. Currently, one must either define their own spacing to match calcite-components (or by extension, TailwindCSS), or integrate TailwindCSS into their project.

Acceptance Criteria

Expose all spacing used by calcite-components through CSS variables.

Relevant Info

No response

Which Component

calcite-components

Example Use Case

A new project uses calcite-components and is not interested in using TailwindCSS. To keep their app looking consistent with calcite-components, they can use CSS variables provided by calcite-components for CSS properties such as padding, margin, right, left, etc.

[jcfranco]

Closing in favor of #7180.