version-snapshot guides alongside API reference, fix index.md links, …

[petesramek]

…add released versions table (#175)

Summary

Previously, versioned folders contained only API reference YAMLs while guide pages were global (unversioned). The root index.md had entirely broken links. The version switcher navigated to a bare /{ver}/ folder that has no index.html, causing 404s on GitHub Pages.

Changes

Workflow (publish-documentation.yml)

• Guide snapshot: copies api-reference/guide/ into api-reference/{ver}/guide/ immediately after API metadata generation, so each version folder contains a full snapshot of both guide and API reference
• DocFX version groups: each group now registers two content entries — API YAMLs (*.yml) and guide pages (guide/*.{md,yml}) — producing _docs/{ver}/ and _docs/{ver}/guide/ in the build output
• Global TOC: Guide nav link now points to {latest}/guide/introduction.html instead of the unversioned guide/
• index.md injection: a single step builds the released versions table and substitutes both {version} and {versions_section} placeholders before docfx build runs (no committed artefacts)

api-reference/api-reference.json

• Removed guide/*.{md,yml} from the global content entry — guide pages now exist only within versioned groups

api-reference/index.md

• Replaced broken links with {version}-placeholder paths resolved at build time
• Added a {versions_section} placeholder that the workflow expands into a full released-versions table

docs-versioning/public/version-switcher.js

• Fixed the fallback navigation branch to resolve the site root via the docfx:rel meta tag and navigate to /{ver}/PolylineAlgorithm.html instead of the bare /{ver}/ folder