[v8.x backport] doc: Backport #19685 and #19949 to v8.x

This backports two documentation changes.

#19685 is a straightforward one and landed cleanly.

#19949 required minor manual formatting adjustments, mostly because it incorporated some unrelated styling fixes for some reason. Main change is the documentation of Buffer.from(Uint8Array) — that behavior is explicitly there since beca3244 (but it also worked before that).

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• documentation is changed or added