improvements to the new row editor

two thing that could be improved for row editor (after hitting `+ Row`) are:
- the keyboard focus always lands on the first column, but this is usually a serial/primary column. Giving the focus to the first column that has not a `DEFAULT` sequence or expression might be better
- when the keyboard focus is on a column with a foreign key, the foreign key selector thing disapeares until the keyboard focus is lost

Start at the row editor opened by the `+ Row` action and reproduce both reported behaviors. Done means focus initially lands on the first column without a DEFAULT sequence or expression, and the foreign-key selector remains visible while that column has keyboard focus.

Written by the indexing model from the issue text.