Docs: use ScssDocs shortcode for Sass utilities API sections

[julien-deramond]

Description

Use the <ScssDocs> shortcode for all the "Sass utilities API" docs sections, matching some .mdx files in v6 and v5 behavior, instead of hand-copied scss snippets that can drift from the source.

• Convert 14 utility docs pages to <ScssDocs>: align-content, align-items, align-self, divide, font-family, font-style, grid, justify-content, justify-items, place-items, pointer-events, space, text-alignment, user-select
• Fix real drift found during conversion: font-family, grid, and user-select had stale snippets that no longer matched scss/_utilities.scss
• Add missing scss-docs marker pairs in scss/_utilities.scss for the utilities above
• Narrow utils-flex to only cover flex/flex-direction/flex-grow/flex-shrink/flex-wrap, matching what flex.mdx documents; split utils-interaction into utils-user-select/utils-pointer-events
• Add a "Sass utilities API" section to aspect-ratio.mdx, which was missing one
• Remove the unused utils-spacing wrapper marker and an orphaned scss-docs-end utils-text comment