parser: fix function as identifier in TiDB is not compatible with Mysql

[djshow832]

What problem does this PR solve?

Issue Number: close #30556

Problem Summary:
Although MySQL declares in https://dev.mysql.com/doc/refman/8.0/en/function-resolution.html that the functions are recognized as functions for create table x(), 4 of them are still recognized as functions:

• ADDDATE and SUBDATE
• SESSION_USER and SYSTEM_USER

Which makes TiDB incompatible with MySQL.

For the case of select x (), it's complicated: TiDB won't report errors for some of them but MySQL does. This incompatibility won't bring any problems. Instead, if we change it, it will break compatibility.

What is changed and how it works?

• Remove the 4 functions from btFuncTokenMap
• Remove builtinAddDate and builtinSubDate

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:

• bb7133
• morgo

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[djshow832]

What do you think of it? Do we merge this PR or do we just update the MySQL tests in the issue? @morgo @tangenta

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/36f602e69b496c3ffe9aa7f3ef12d4ed916f60a5

[morgo]

What do you think of it? Do we merge this PR or do we just update the MySQL tests in the issue? @morgo @tangenta

LGTM. It is hard to predict users with reserved words, so I think it is worth making it more compatible.

[bb7133]

LGTM

[bb7133]

PTAL @morgo

[djshow832]

/merge

[ti-chi-bot]

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

Commit hash: b0a4be4