fix(cdc): fix wrong default column matching

[KeXiangWang]

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What's changed and what's your intention?

Fix the bug introduced in #19354. Resolve #20346
The bug will cause two problems:

1. Differences in the orders of rw schema and pg schema can lead to wrong default value assigned.
2. Due to zip_eq_fast, if the numbers of columns in rw schema and pg schema are different, panic happens.

Checklist

• I have written necessary rustdoc comments.
• I have added necessary unit tests and integration tests.
• I have added test labels as necessary.
• I have added fuzzing tests or opened an issue to track them.
• My PR contains breaking changes.
• My PR changes performance-critical code, so I will run (micro) benchmarks and present the results.
• My PR contains critical fixes that are necessary to be merged into the latest release.

Documentation

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Release note

[BugenZhao]

Rest LGTM

[BugenZhao]

Is it possible that we don't find a column in external_columns? Should we return an error (just like in #20203)?

[KeXiangWang]

I cannot find a case for now. But a potential case is #19112.
An example haven't been supported but to be supported:

CREATE TABLE test (
    id int,
    name varchar,
    my_id int as id + 1, // generated column
    PRIMARY KEY (id)
) FROM pg_source TABLE 'public.test';

I can make it throw an error for now.

[KeXiangWang]

Updated

[KeXiangWang]

The same logic can be found here, so it's also OK not to throw an error.