feat(StoneDB 8.0): st_select_lex::set_join is deleted in mysql8.0. (#598)

[lujiashun]

Summary about this PR

Issue Number: close #598

1 in the commit(commit1) below, st_select_lex::set_join is renamed as SELECT_LEX::set_join
mysql/mysql-server@74f720b
2 in the commit(commit2) below, SELECT_LEX::set_join is deleted:
mysql/mysql-server@03b579f
3 in commit2, it is given the reference to implement the set_join:

old version	new version
set_join(join_local);	thd->lock_query_plan(); join = join_local; thd->unlock_query_plan();

4 by the way, comment of variable Query_block::join is like this:

  /**
    After optimization it is pointer to corresponding JOIN. This member
    should be changed only when THD::LOCK_query_plan mutex is taken.
  */
  JOIN *join{nullptr};

5 So, use LOCK_query_plan mutex to implement set_join is a proper way.

Tests Check List

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

Changelog

• New Feature
• Bug Fix
• Improvement
• Performance Improvement
• Build/Testing/CI/CD
• Documentation
• Not for changelog (changelog entry is not required)

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features

[mergify]

Thanks for the contribution!
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[DandreChen]

LGTM.

[RingsC]

LGTM

[mergify]

Thanks for the contribution!
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Please review the labels and make any necessary changes.