expression: fix wrong result type for greatest/least

[SeaRise]

What problem does this PR solve?

Issue Number: close #30261

Problem Summary:
When arguments of greatest/least are mixed with temporalType and string, tidb will
1、Convert all args as String
2、EvalString to get arg value
3、Parse string as datetime. If it's a valid datetime, use string(datetime) to compare. Otherwise use the result of EvalString to compare.

But it is not compitable with mysql
1、if { arg.is_temporal, EvalTime to get arg value (https://github.com/mysql/mysql-server/blob/8.0/sql/item_cmpfunc.cc#L1498) } else { EvalString to get arg value, and parse string to MYSQL_TIMESTAMP_DATE/MYSQL_TIMESTAMP_DATETIME(https://github.com/mysql/mysql-server/blob/8.0/sql/item_func.cc#L3667-L3678, https://github.com/mysql/mysql-server/blob/8.0/sql/item_cmpfunc.cc#L1520-L1524) }
2、compare with time value (https://github.com/mysql/mysql-server/blob/8.0/sql/item_func.cc#L3708)
3、if there any err, use the result of EvalString to compare (https://github.com/mysql/mysql-server/blob/8.0/sql/item_func.cc#L3745-L3748)

What is changed and how it works?

Port the code of https://github.com/mysql/mysql-server/blob/8.0/sql/item_cmpfunc.cc#L1520-L1524

TODO:
When arguments of greatest/least are mixed with time, duration, string, the result is not compitable with mysql.
Such as SELECT GREATEST(cast('000:59:59' as time), cast('2000' as YEAR), '2002-01-01');

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

fix wrong result type for greatest/least

[ti-chi-bot]

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[SeaRise]

fixed by #31037