tidb: Remove warning about experimental feature for collecting predicate columns and update default value for tidb_enable_collect_predicate_columns

[Oreoxmt]

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What is changed, added or deleted? (Required)

tidb: Remove warning about experimental feature for collecting predicate columns and update default value for tidb_enable_collect_predicate_columns

Which TiDB version(s) do your changes apply to? (Required)

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By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions (in Chinese).

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 versions)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)

What is the related PR or file link(s)?

• This PR is translated from: tidb: Remove warning about experimental feature for collecting predicate columns and update default value for tidb_enable_collect_predicate_columns docs#19905
• Other reference link(s):

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[Oreoxmt]

/cc @Rustin170506

[Oreoxmt]

@Rustin170506 PTAL

[qiancai]

Removed the needs-cherry-pick-release-8.3 label because the v8.3 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v8.3 and will no longer receive new updates.

[qiancai]

Removed the needs-cherry-pick-release-8.4 label because the v8.4 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v8.4 and will no longer receive new updates.

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-07-31 07:05:10.726210254 +0000 UTC m=+161323.411480470: ☑️ agreed by qiancai.

[0xPoe]

Thanks!

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[Oreoxmt]

/approve

[ti-chi-bot]

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #20711.