doc: correct default highWaterMark values

[umuoy1]

The fs.createWriteStream() and filehandle.createWriteStream() docs still listed a fixed 16 KiB default. These streams inherit the default byte-stream highWaterMark, which is 64 KiB on non-Windows platforms and 16 KiB on Windows.

Update the fs docs to reference stream.getDefaultHighWaterMark() and clarify the platform-specific defaults in the stream docs.

[umuoy1]

Gentle ping @nodejs/documentation — could someone take a look?

[nodejs-github-bot]

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----------------------------------- PR info ------------------------------------
Title doc: correct default highWaterMark values (#64617)
Author Yilong Li <burningdian@gmail.com> (@umuoy1)
Branch umuoy1:doc-correct-write-stream-high-water-mark -> nodejs:main
Labels doc, stream, author ready
Commits 3
- doc: correct default highWaterMark values
- Merge branch 'main' into doc-correct-write-stream-high-water-mark
- doc: add highWaterMark change history
Committers 2
- umuoy1 <burningdian@gmail.com>
- GitHub <noreply@github.com>
PR-URL: https://github.com/nodejs/node/pull/64617
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/64617
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
--------------------------------------------------------------------------------
ℹ This PR was created on Mon, 20 Jul 2026 09:05:52 GMT
✔ Approvals: 1
✔ - Chengzhong Wu (@legendecas) (TSC): https://github.com/nodejs/node/pull/64617#pullrequestreview-4849836694
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Auto-merging doc/api/fs.md
CONFLICT (content): Merge conflict in doc/api/fs.md
Auto-merging doc/api/stream.md
error: could not apply 1f4ac06ce5... doc: correct default highWaterMark values
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✘ Failed to apply patches

https://github.com/nodejs/node/actions/runs/30921412978

[nodejs-github-bot]

Landed in e535675