[BUG] Replace duplicated aggregation logic with `aggregateWithTrimming()`

[ishaoxy]

What is the bug?
In the current implementation of buildStreamWindowJoinPlan in the Streamstats command, the aggregation for window functions was partially re-implemented inside this method. But we should just use aggregateWithTrimming() to avoid duplicating existing functionality.

How can one reproduce the bug?
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

What is the expected behavior?
A clear and concise description of what you expected to happen.

What is your host/environment?

• OS: [e.g. iOS]
• Version [e.g. 22]
• Plugins

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Do you have any additional context?
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