Convert `Variance Sample` to UDAF

[jayzhan211]

Is your feature request related to a problem or challenge?

Part of #8708

1. Move variance aggregate expression in datafusion/physical-expr/src/aggregate/variance.rs to functions-aggregate.
2. Add expression api in roundtrip_expr_api in datafusion/proto/tests/cases/roundtrip_logical_plan.rs

Similar to #10372 #10418

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[yyin-dev]

take