fix(output-mapping): clarify column swap validation errors

[OlenaMarchuk]

Summary

AbstractTableStructureValidator::validateColumnsName() reported only one half of the mismatch, which made real failures misleading. Production job 1325273716 failed with:

Table "in.c-keboola-ex-db-mysql.magazine_posts" does not contain columns: "title_square_image".

The actual cause was a column swap in the source (one column replaced by another): a column disappeared from the schema, so the counts matched and the new column could not be auto-added. Read literally, the old message points at the added column and hides the blocker.

Both throws now also list array_diff($tableColumns, $schemaColumnsNames) — the columns that exist in the table but not in the schema — and the swap case explains that renames/replacements are not applied automatically:

Table "…" does not contain columns: "title_square_image". Columns "title_image" are present in the
table but missing in the schema. This usually means a column was renamed or replaced; such a change
cannot be applied automatically. Drop the obsolete columns from the table — the new ones will be
added on the next run.

Note the control flow this relies on: the does not contain columns throw is reachable only when column counts are equal and the diff is non-empty (always a swap), and the same number of columns throw only when the table has columns absent from the schema — so the appended list is never empty. No behaviour change; the missing-columns auto-add path is untouched.

Link to Devin session: https://app.devin.ai/sessions/cd95e73b195c46c4abeea2af594577e8
Requested by: @OlenaMarchuk

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