Allow field name declaration in ROW literal

[dain]

Description

Add support for row(a 1, b 2) instead of the much more complex cast(row(1, 2) as row(a integer, b integer)). The old syntax is particularly annoying because you have to repeat the types for the fields.

Release notes

(X) Release notes are required, with the following suggested text:

## General
* Allow field name declaration in ROW literal.  For example, `row(a 1, b 2)` is now legal. ({issue}`issuenumber`)