Fixed #36947 -- Avoided column alteration for db_comment-only changes. - #21331

Trac ticket number

ticket-36947

Branch description

This branch introduces support for standalone COMMENT ON COLUMN statements on PostgreSQL and Oracle when only a column comment changes. This avoids unnecessary ALTER COLUMN operations, reducing lock severity (SHARE UPDATE EXCLUSIVE instead of ACCESS EXCLUSIVE) and preventing migration failures involving GeneratedFields or columns backed by database views, while preserving the existing fallback behavior for other backends.

AI Assistance Disclosure (REQUIRED)

• No AI tools were used in preparing this PR.
• If AI tools were used, I have disclosed which ones, and fully reviewed and verified their output.

Used GPT-5.5 for initial test structure and code review. All code was reviewed, tested, and verified manually.

Checklist

• This PR follows the contribution guidelines.
• This PR does not disclose a security vulnerability (see vulnerability reporting).
• This PR targets the main branch.
• The commit message is written in past tense, mentions the ticket number, and ends with a period (see guidelines).
• I have not requested, and will not request, an automated AI review for this PR.
• I have checked the "Has patch" ticket flag in the Trac system.
• I have added or updated relevant tests.
• I have added or updated relevant docs, including release notes if applicable.
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