fix: add scrollbar gutter to style macro

[yihuiliao]

kept getting a maximum depth exceeded error after i merged main into this #10600 for one specific story (which is stashed so it's not actually on the PR). this is bc the scrollbar kept appearing and disappearing, affecting the layout.

turns out in https://github.com/adobe/react-spectrum/pull/10577/changes i had moved scrollbarGutter which was previously inline to the style macro but it's not supported there so it was silently failing. this PR adds scrollbarGutter to the style macro theme. if we do not want to support this, we can just add it back to GridList's inline styles.

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices
• I understand every change in this PR and can explain why it's there.
• If AI-assisted, I followed our AI contribution guidance and pointed my assistant at AGENTS.md.

📝 Test Instructions:

go to Chat stories and make sure scrollbarGutter: stable is applied to the GridList styles

🧢 Your Project:

[snowystinger]

I forget if position in the object matters, might need to be added to the end

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the S2 docs
• View the React Aria docs

[rspbot]

Agent Skills Changes

Modified (11)

• react-aria/agent-skills/index.json $\color{green}{+1}$ $\color{red}{-1}$
• react-aria/agent-skills/react-aria.tar.gz
• react-aria/agent-skills/react-aria/references/components/Separator/useSeparator.md $\color{green}{+1}$ $\color{red}{-1}$
• s2/agent-skills/index.json $\color{green}{+3}$ $\color{red}{-3}$
• s2/agent-skills/migrate-react-spectrum-v3-to-s2.tar.gz
• s2/agent-skills/migrate-react-spectrum-v3-to-s2/references/docs-style-macro.md $\color{green}{+1}$
• s2/agent-skills/react-spectrum-s2.tar.gz
• s2/agent-skills/react-spectrum-s2/references/guides/ai-components.md $\color{red}{-17}$
• s2/agent-skills/react-spectrum-s2/references/guides/style-macro.md $\color{green}{+1}$
• s2/agent-skills/react-spectrum-s2/references/react-aria/components/Separator/useSeparator.md $\color{green}{+1}$ $\color{red}{-1}$
• s2/agent-skills/spectrum-audit.tar.gz

Install

React Spectrum S2:

npx skills add https://d1pzu54gtk2aed.cloudfront.net/pr/cc0d69a88392673879af810eac8d4916f9c6755e/

React Aria:

npx skills add https://d5iwopk28bdhl.cloudfront.net/pr/cc0d69a88392673879af810eac8d4916f9c6755e/