Allow calculated fields to be entered as text input in Datastream mapping

[#1]

This feature would recognize valid functions/syntax for calculated fields when entered as text input in the mapping interface and treat them as the calculated field data type.

Currently, Datastream mapping does not allow you to input calculated field functions as regular text input in a source field. The function does not work and the data is not passed into the target field when doing so. Instead, you must enter the calculated field through its own UI.

This means that you cannot update an existing source field to use a simple function like lower(), for example. Rather, you must delete the existing mapping and recreate it through the calculated field UI.

Even after creating a calculated field through the UI, you cannot paste that same field in other source fields. This means, in order to use the same calculated field for multiple mappings, you must recreate the calculated field every time.

Creating this feature would improve mapping efficiency and prevent mistakes.