Throw error in alter table set default if default fails rule(s)

[druvv]

This PR makes alter column set default error when its default expression fails the default expression rules. Previously the DDL succeeded and when an insert or any other query was performed the default would cause a continuous error.

alter table t alter column col1 set default '{\"bye\":1}'
-- errors with: TEXT, BLOB, GEOMETRY, and JSON types may only have expression default values

[fulghum]

Looks good! Nice fix! ✨