Add tiflash supported pushdown for vector functions (#18901)

[ti-chi-bot]

This is an automated cherry-pick of #18901

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• v8.4 (TiDB 8.4 versions)
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What is the related PR or file link(s)?

• This PR is translated from: Add tiflash supported pushdown for vector functions docs#19194
• Other reference link(s): TiDB vector search doc #18502, expression: Add vector functions tidb#55021

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

[qiancai]

/approve

[ti-chi-bot]

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