expression: convert charset by wrapping internal builtin function

[tangenta]

What problem does this PR solve?

Problem Summary: Close #29863.

This is a refactoring PR. The code changes about built-in functions in TiKV can be minimized.

After the investigation about several built-in functions, I found some common patterns:

1. Create a new encoding.
2. Convert the arguments into new charset from utf8.
3. Apply these changes to the vectorized-version evaluation.

We can extract these patterns into another Sig named builtinToBinarySig(to_binary()) and wrap the cast function as follows:

The rewrite process before this PR:

select some_builtin(arg1, arg2...)

is rewritten to

select some_builtin(cast_as_string(arg1), cast_as_string(arg2)...)

The rewrite process after this PR:

select some_builtin(arg1, arg2...)

is rewritten to

select some_builtin(to_binary(cast_as_string(arg1)), to_binary(cast_as_string(arg2))...)

Then we can maintain a built-in function list to determine which function needs to be wrapped, instead of putting the boilerplates everywhere.

var toBinaryMap = map[string]struct{}{
	ast.Hex: {}, ast.Length: {}, ast.OctetLength: {}, ast.ASCII: {},
	ast.ToBase64: {},
}

What is changed and how it works?

See the code.

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:

• xiongjiwei
• zimulala

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[xiongjiwei]

/run-check_dev_2

[zimulala]

How about other functions like upper？

[tangenta]

Let's add them later in the next PR.

[zimulala]

LGTM

[tangenta]

/merge

[ti-chi-bot]

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

Commit hash: 41263b9

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