sql: column_default in information_schema.columns is incompatible with postgres

[knz]

Describe the problem

The content of column_default is using a format that confuses postgres-compatible apps.
(Found here)

There are 2 different problems:

1. its syntax uses type annotations where none are expected.
2. the type annotation is also incompatible with the actual type of the column.

To Reproduce

In PostgreSQL:

> create table mytable(x smallint default 0);
> select data_type, column_default  from information_schema.columns where table_name = 'mytable' and column_name = 'x';
 data_type | column_default
-----------+----------------
 smallint  | 0

In CockroachDB:

> create table mytable(x smallint default 0);
> select data_type, column_default  from information_schema.columns where table_name = 'mytable' and column_name = 'x';
  data_type | column_default
------------+-----------------
  smallint  | 0:::INT8

cc @rafiss for triage.

Jira issue: CRDB-19526

Epic CRDB-17785

[rafiss]

#94153 resolves this

[knz]

fixed by #94153 indeed