[MBQL lib] Add `column-extractions` to the top level (#41525)

Column extractions are "canned" expressions based on a column's
type. For example, we might extract the weekday from a temporal column,
or the domain from an email or URL column.

This logic already existed inside the `column-extract` drill; this pulls
it out as a top-level concept, since extractions are also being
integrated into the notebook editor apart from drills.

Part of the follow-up for Extract Column epic #38964.