Support using insertSelect with an entire Entity

[isomorpheme]

Sometimes I want to insert entire entities into a table, from a SELECT query, including the primary key.¹ As far as I can tell, this isn't possible with the current insertSelect & Insertion API - the PersistEntity constraint and the types of (<#) and (<&>) get in the way.

The easiest way to support this is probably with an extra insertSelectEntity, to parallel insertEntityMany from Persistent. I haven't yet tried to come up with a safe type for such a function.

Footnotes

1. My use case right now actually involves a REPLACE, as in Support replaceSelect #86, but it's otherwise the same idea. ↩