Fix submenu safe area edge case

[reidbarber]

For RSP and RAC submenus.

There was an edge case where the submenu may close unexpectedly. To reproduce it, you could:

1. Move your pointer over the trigger item, then down to the submenu
2. Move your pointer back to the trigger item, but immediately back out to the submenu when the trigger was entered.

A stale previous pointer position state was being used, so the pointer movement angle used was inaccurate, so the submenu closed. Now that we properly reset the previous pointer position, this doesn't occur.

Previous (broken) behavior:

broken.mov

New (working) behavior:

working.mov

✅ 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:

Try the reproduction steps above in RAC and RSP submenu stories.

🧢 Your Project:

[rspbot]

Build successful! 🎉

• View the storybook
• View the storybook-17
• View the storybook-16
• View the documentation

[snowystinger]

this feels much better, nice find!

[yihuiliao]

lgtm

[rspbot]

Build successful! 🎉

• View the storybook
• View the storybook-17
• View the storybook-16
• View the documentation

[rspbot]

## API Changes

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