Composite types for updatable views

While simple views are automatically updatable [1], this does not extend to
composite types; that is, if a view constructs a composite type for one or
more columns, this column then is not updatable:

> A column is updatable if it is a simple reference to an updatable column
of the underlying base relation

It would seem simple enough to support composite types if the view column
is constructed using row expression in which each field is "a simple
reference to an updatable column".

As a practical example, this could enable geometric types being exposed at
the view layer, but supported in an underlying table by primitive types.

[1]
https://www.postgresql.org/docs/current/sql-createview.html#SQL-CREATEVIEW-UPDATABLE-VIEWS