rendering.components.form: Rewrite form data extraction to use select()
rendering.components.form: Rewrite form data extraction to use select()

The new select() facility suits form's requirements perfectly, no need
to do horrendous tree reconstruction through a Cartesian product.  This
also shifts the burden of unpacking and mapping data values to form
client.

edgedb/edgedb,edgedb/edgedb,edgedb/edgedb