[core] Updating export of design tokens, adding dark theme

[mm-wang]

Changes proposed in this pull request:

• Change to build folder name
• Adding an export of design-tokens.css to @blueprintjs/core

Reviewers should focus on:

Build compiles

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• Improvement (Improving existing functionality)
• Fix (Fixing an issue with existing functionality)
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Description

[core] Tweaks to export of design tokens

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[svc-palantir-github]

[Design Tokens] Add a new export file for just design tokens into blueprintjs/core

Build artifact links for this commit: documentation | landing | table | demo

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💡 Improvements

• [core] Tweaks to export of design tokens (#7736)

[svc-palantir-github]

Updating pnpm lock

Build artifact links for this commit: documentation | landing | table | demo

This is an automated comment from the deploy-preview CircleCI job.