Fixed #25947 -- Query's str() method worked normally when 'default' database is empty

[jayvynl]

sql_with_params, build_lookup and is_nullable in Query would use the correct connection and generate more reasonable SQL.

Trac ticket number

ticket-25947

Branch description

This fix makes output of print(queryset.query) more reasonable when the queryset use a different database from default.

Checklist

• This PR targets the main branch.
• The commit message is written in past tense, mentions the ticket number, and ends with a period.
• 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.
• For UI changes, I have attached screenshots in both light and dark modes.

[github-actions]

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