[Lens] Bugs in table rendering caused by toExpression function

[wylieconlon]

The table configuration should always be matched in the table expression, which is not happening for in several cases.

Steps to reproduce:

1. Use the chart switcher and go to an empty datatable
2. Drag the Records field and you should get a suggestion with 2 columns
3. Drag a new string field into the empty dimension labeled "Drop a field here"
4. The order shown in the table will not match the order shown on the right side

The fix for this issue should be to use the same logic in both getConfiguration and toExpression, which is to sort the table columns by the datasource order using this snippet from getConfiguration.

    const datasource = frame.datasourceLayers[layer.layerId];
    const originalOrder = datasource.getTableSpec().map(({ columnId }) => columnId);
    // When we add a column it could be empty, and therefore have no order
    const sortedColumns = Array.from(new Set(originalOrder.concat(layer.columns)));

This small change should fix the bug and guarantee consistent order.

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)