planner: fix the issue that planner may cache invalid plans for joins in some cases (#28432)

[ti-srebot]

cherry-pick #28432 to release-5.1
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/28446

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---

What problem does this PR solve?

Issue Number: close #28087, #28162

Problem Summary: planner: fix the issue that planner may cache invalid plans for joins in some cases

What is changed and how it works?

The root cause is that the planner cannot distinguish different parameters when eliminating duplicated DNF conditions.
For example, the DNF col=1 or col=1 can be converted to col=1 in this elimination and it is correct.
But when values in conditions are parameters instead of constants, the planner may make some wrong eliminating operations since it cannot distinguish different parameters. For example, col=@a or col=@b may be converted to col=@a.

This PR updates the encoding method of expressions to make the planner can distinguish different parameters.

Check List

Tests

• Unit test

Release note

planner: fix the issue that planner may cache invalid plans for joins in some cases

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Reminiscent
• rebelice

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[ti-srebot]

/run-all-tests

[ti-srebot]

@qw4990 you're already a collaborator in bot's repo.

[Reminiscent]

/merge

[ti-chi-bot]

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

Commit hash: 305626c

[hawkingrei]

/run-mysql-test

[hawkingrei]

/run-mysql-test

[hawkingrei]

/run-mysql-test

[bb7133]

/merge

[hawkingrei]

/run-mysql-test

[ti-chi-bot]

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