feat: rework scroll utilities and fix layout bugs

[nwidynski]

Closes no issues directly, because this PR is intentionally limited to additions only. Migrating call sites to the new utilities and signatures is to be done in chore follow-ups, because it would otherwise be rather hard to review what changed here.

From a high level, this is the first round of changes for a set of layout- and drastically improved scroll utilities. Here is what this PR does today:

1.) Fix issues in getScrollParent and getScrollParents by merging their implementation into a new generator
2.) Fix various bugs in isScrollable and expand its scope for window scrolling
3.) Introduce modalities and axis isolation into scroll utilities (pointer-> skip hidden, virtual -> incl. hidden)

The rest is just chores of moving code blocks from calculatePosition and domHelpers.

✅ 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 CLAUDE.md.

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