fix(S2): Allow custom widths on CustomDialogs

[yihuiliao]

Closes

✅ 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

📝 Test Instructions:

Go to the CustomWidth story and confirm that it looks alright and the width is indeed custom. Also confirm that the other dialogs look alright. One thing to note is that you cannot mix the prop size with a custom width or else it will look funkyyy but I think that's fine since you probably wouldn't be using a default size if you want to use a custom width.

🧢 Your Project:

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the documentation
• View the S2 docs

[LFDanLu]

Mind running chromatic on this? Probably won't pick anything up since the change was just for allowing through an override but just in case