Passing relation metadata to Exec routine

While working on Pluggable TOAST [1] we found out that creation

of new relation with CREATE TABLE AS... or CREATE TABLE LIKE -

method

does not receive any metadata from columns or tables used in query

(if any). It makes sense to pass not only column type and size, but

all other metadata - like attoptions,base relation OID (and, maybe,

reloptions), if the column from existing relation was used. 

A good example is the creation of new relation from base one where

some other Toaster was assigned to a column - it seems reasonable

that the same column in new table must have the same Toaster assigned

as the base one. And we already have a couple of other practical uses

for the metadata passed along with column definitions.

Any thoughts or suggestions?

[1] https://commitfest.postgresql.org/41/3490/