Add Schema Constraint for Intersect, Difference, and Other Operators

[aahei]

During the review of PR #1924, we found that the following operators which take input from multiple sources require that the schema for the sources be the same, but currently do not check this constraint in the front-end. Adding this constraint can help users to find errors in their workflows.

In these operators, the schema of their input sources should be the same.

• Symmetric Difference
• Distinct
• Intersect
• Difference
• Union

[Yicong-Huang]

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