add _tidb_rowid document (#21446)

[ti-chi-bot]

This is an automated cherry-pick of #21446

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• This PR is translated from: add _tidb_rowid document docs#22572
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• Delete files
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• Might cause conflicts after applied to another branch

[ti-chi-bot]

@hfxsd This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[ti-chi-bot]

@ti-chi-bot: ## If you want to know how to resolve it, please read the guide in TiDB Dev Guide.

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[hfxsd]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hfxsd

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