Change partial aggregation symbols for variance and standard deviation aggregators.

[Sh-Zh-7]

Description

IoTDB uses TypeProvider class to identify type by given symbol. And aggregators have two output types, one for partial output, another for final output.

In variance and standard deviation aggregators, the two types are different. The partial output type is TEXT while the final output type depends on user's input, which can be INT, FLOAT and so on.

However, current implementation outputs same symbols for both partial and final aggregators for variance and standard deviation. And this may cause some unexpected behaviors like the final output type can be overrided by partial output type.

This PR adds _partial suffix to partial output symbol in order to distinguish from final output symbol. Notice there is no need to add new integration tests for this scenario, since #11581 already add GROUP BY LEVEL in specific test file, which
has covered this problem.

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This PR has:

• been self-reviewed.
• been tested in a test IoTDB cluster.