Theme: Add Figma scopes to element size tokens

[jameskoster]

Follow up to #76545.

What

Adds com.figma.scopes of WIDTH_HEIGHT to the wpds-dimension.size.* element size tokens (5xs through lg) in packages/theme/tokens/dimension.json.

Why

Without a Figma scope defined as an $extensions entry, these tokens aren't surfaced as size options in Figma's variable pickers when designers are sizing layers.

Adding the WIDTH_HEIGHT scope makes them importable and selectable in the appropriate context, consistent with how the existing surface-width tokens are scoped.

How

• Added an $extensions block with "com.figma.scopes": [ "WIDTH_HEIGHT" ] to each of the eight size tokens, mirroring the established pattern already used by surface-width.
• No value or naming changes — purely additive metadata, so there is no impact on the generated CSS custom properties or any consuming code.

Testing Instructions

1. Import packages/theme/tokens/dimension.json into Figma.
2. Confirm the wpds-dimension/size/* variables import with the WIDTH_HEIGHT scope applied.
3. When sizing a layer (width/height), confirm the size tokens are offered in the variable picker.

Note

Unfortunately Figma's scoping system doesn't support targeting height or width individually, only both together, so despite it not matching their intended purpose it will be possible to assign size tokens to widths in Figma.

[github-actions]

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Co-authored-by: jameskoster <[email protected]>
Co-authored-by: ciampo <[email protected]>

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[aduth]

Aside: We should document how we're using Figma scopes in these token source files. At the very least it would be a useful resource to point to https://developers.figma.com/docs/plugins/api/VariableScope/ as the reference of what's available.

[aduth]

Aside: We should document how we're using Figma scopes in these token source files. At the very least it would be a useful resource to point to https://developers.figma.com/docs/plugins/api/VariableScope/ as the reference of what's available.

Follow-up: #79157