Improve watermark error and show watermark columns in explain

[fuyufjh]

Is your feature request related to a problem? Please describe.

...be executed in Emit-On-Window-Close mode.
HINT: Please make sure there is one and only one watermark column in GROUP BY

This error is unfriendly to users because they don't know the derivation rule of watermark.

I am considering to show the watermark columns in explain, and guide the users to check their queries in the above error message.

Describe the solution you'd like

No response

Describe alternatives you've considered

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Additional context

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[stdrc]

We now have output_watermarks field in each plan node in explain, and after #19894 and #19998, this kind of error message won't happen as often as before.