Backport: [v6.0] fix(ai): return validated elements from array output parseCompleteOutput

[github-actions]

This is an automated backport of #16791 to the release-v5.0 branch. FYI @gr2m
This backport has conflicts that need to be resolved manually.

git cherry-pick output

Auto-merging packages/ai/src/generate-text/output.test.ts
CONFLICT (content): Merge conflict in packages/ai/src/generate-text/output.test.ts
Auto-merging packages/ai/src/generate-text/output.ts
CONFLICT (content): Merge conflict in packages/ai/src/generate-text/output.ts
error: could not apply 45a9cbf52b... [v6.0] fix(ai): return validated elements from array output parseCompleteOutput (#16791)
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