bug: frontend panics when creating a cdc table with partial columns specified

[BugenZhao]

Describe the bug

The frontend node will panic if user's going to create a CDC table with partial columns specified.

Error message/log

dev=> create table tttt (k int primary key) from pg_source table 'public.tttt';
ERROR:  Panicked when handling the request: assertion `left == right` failed
  left: 1
 right: 2
This is a bug. We would appreciate a bug report at:
  https://github.com/risingwavelabs/risingwave/issues/new?labels=type%2Fbug&template=bug_report.yml
server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.

To Reproduce

In upstream Postgres:

create table tttt (k int primary key, v int);

In RisingWave:

dev=> create source pg_source with (
 connector = 'postgres-cdc',
 hostname = 'localhost',
 port = '5432',
 username = 'bugenzhao',
 password = '',
 database.name = 'postgres',
 slot.name = 'pg_slot'
);
CREATE_SOURCE
dev=> create table tttt (k int primary key) from pg_source table 'public.tttt';
ERROR:  Panicked when handling the request: assertion `left == right` failed
  left: 1
 right: 2
This is a bug. We would appreciate a bug report at:
  https://github.com/risingwavelabs/risingwave/issues/new?labels=type%2Fbug&template=bug_report.yml
server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.

Expected behavior

Not panic but accept with verification on the validity of user specified partial schema.

How did you deploy RisingWave?

No response

The version of RisingWave

main

Additional context

Panicked at:

risingwave/src/frontend/src/handler/create_table.rs

Lines 1194 to 1199 in f0db87b

	for (col, external_col) in
	columns.iter_mut().zip_eq_fast(external_columns.into_iter())
	{
	col.column_desc.generated_or_default_column =
	external_col.column_desc.generated_or_default_column;
	}

Seems to be introduced by #19354. Unreleased as for now. Released versions work correctly.

[BugenZhao]

Let's see if we can reuse some code of #20203