expression: fix querying cluster tables reports regexp is not supported

[djshow832]

What problem does this PR solve?

Issue Number: close #32783

Problem Summary:
When query cluster tables with regexp function, an error happens: FUNCTION RegexpUTF8Sig does not exist.

This is because once regexp is supported by TiFlash, TiDB pushes down the operator to other TiDB instances, but on the TiDB side, regexp doesn't support being converted from a pb to an expression signature.

What is changed and how it works?

One way is not to push down regexp to another TiDB instance, which is the same as before, but it's slower and needs more changes.
In this PR, I supported converting it from a pb to an expression signature.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• breeswish
• crazycs520

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[breezewish]

Thanks. cc @crazycs520

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/102b4ffb92294f262fee90d488abd135fea9e67c

[crazycs520]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 75a2236

[ti-chi-bot]

@djshow832: Your PR was out of date, I have automatically updated it for you.

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/run-all-tests

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