Improve usability and docs for UpdateBy

[lbooker42]

After this change should be able to call updateBy without needing explicit imports. Some examples:

import io.deephaven.api.updateby.UpdateByClause;
import static io.deephaven.api.updateby.UpdateByClause.*;

cumulative_sum=emptyTable(10).update("RowNum=ii").updateBy(UpdateByClause.of(CumSum("RowNumSum=RowNum")))

cumulative_sum_grouped=emptyTable(10).update("RowNum=ii", "Group=RowNum%3").updateBy(UpdateByClause.of(CumSum("RowNumSum=RowNum")), "Group")

cumulative_multi_grouped=emptyTable(10).update("RowNum=ii", "Group=RowNum%3").updateBy([UpdateByClause.of(CumSum("RowNumSum=RowNum")), UpdateByClause.of(CumMin("RowNumMin=RowNum"))], "Group")

can be written as

cumulative_sum=emptyTable(10).update("RowNum=ii").updateBy(CumSum("RowNumSum=RowNum"))

cumulative_sum_grouped=emptyTable(10).update("RowNum=ii", "Group=RowNum%3").updateBy(CumSum("RowNumSum=RowNum"), "Group")

cumulative_multi_grouped=emptyTable(10).update("RowNum=ii", "Group=RowNum%3").updateBy([CumSum("RowNumSum=RowNum")),CumMin("RowNumMin=RowNum")], "Group")

Closes #2647