Add tiflash supported pushdown for vector functions

[JaySon-Huang]

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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-cn#18901
• Other reference link(s): update vector search docs #18779, 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

[JaySon-Huang]

/cc @EricZequan @breezewish

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-10-28 07:49:50.686554406 +0000 UTC m=+249703.525709949: ☑️ agreed by qiancai.
• 2024-10-28 07:52:56.559968798 +0000 UTC m=+249889.399124336: ☑️ agreed by Oreoxmt.

[qiancai]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.4: #19224.