docs: Server functions rename

[icyJoseph]

Closes: https://github.com/vercel/next.js/issues/86781

[github-actions[bot]]

All broken links are now fixed, thank you!

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #86827 will not alter performance

_{Comparing docs/server-functions-update (cf3d6da) with canary (1a1957c)}

Summary

✅ 17 untouched
⏩ 3 skipped[^skipped]

[^skipped]: 3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports.