docs(block-kit): refine design guidance

[wgminer]

Summary

• incorporate focused data visualization guidance into data-display-design.md
• make the new design references more consistent and direct, with implementation details separated from design guidance
• add an Approval Set pattern and align the Approval Message pattern with the guidance

This is a focused follow-up to #167. Merging it adds the commit to the block-kit-design-references branch and therefore updates #167.

Validation

• make lint
• make test-unit (21 passed)

[changeset-bot]

🦋 Changeset detected

Latest commit: 95354ec

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
slack	Patch

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[salesforce-cla]

Thanks for the contribution! Unfortunately we can't verify the commit author(s): Will Miner <w***@s***.com>. One possible solution is to add that email to your GitHub account. Alternatively you can change your commits to another email and force push the change. After getting your commits associated with your GitHub account, sign the Salesforce Inc. Contributor License Agreement and this Pull Request will be revalidated.

[wgminer]

Closing this version so I can replace the blanket use of ‘people’ with contextually natural product language and reopen a clean review.