expression: make infer collation support the expressions with different charset

[xiongjiwei]

What problem does this PR solve?

Problem Summary:

• add a struct ExprCollation, it holds all the collation-related information to avoid function return to many values.
• some tests only have collation but do not have charset, add the charset information into it.
• add repertoire field into collationInfo, see https://dev.mysql.com/doc/refman/8.0/en/charset-repertoire.html.
• refactor inferCollation logic, make it totally same with DTCollation::aggregate in MySQL.
• add safeConvert after inferring collation to check if all the arguments can convert their charset to the derived charset safely

this PR changes a lot, but most of them are simply replace, reviewers should force on expression/collation.go

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:

• tangenta
• zimulala

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[zimulala]

LGTM

[zimulala]

/merge

[ti-chi-bot]

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

Commit hash: fa0c3b9

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