refactor: refactor merge into optimizer and fix unexpected distribution plan

[xudong963]

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Summary

1. support explain pipeline merge into
2. support explain fragments merge into
3. reduce the occurrence of *distributed && !*change_join_order
4. inner join can directly use broadcast join, don't need to add RowNumber operator
5. reduce the complexity of merge into optimizer.
6. improve merge into distribution plan, see the file tests/sqllogictests/suites/mode/cluster/merge_into_non_equal_distributed.test

• Fixes #[Link the issue here]

Tests

• [ ] Unit Test
• [x] Logic Test
• [ ] Benchmark Test
• [ ] No Test - Explain why

Type of change

• [x] Bug Fix (non-breaking change which fixes an issue)
• [ ] New Feature (non-breaking change which adds functionality)
• [ ] Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• [ ] Documentation Update
• [x] Refactoring
• [ ] Performance Improvement
• [ ] Other (please describe):

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This change is