fix: support custom focus targets in DateRangePicker

[ZedingZhang]

Closes #5766

DateRangePicker focus handlers currently default their event target to Element, which makes them incompatible with form libraries whose handlers use FocusEvent<HTMLElement>. This change allows consumers to provide a focus event target type while retaining Element as the default for backward compatibility.

The target generic is propagated only through the types required by DateRangePicker: the shared stately date picker base, range picker state options, useDateRangePicker, and the React Aria Components DateRangePicker. DateField, DatePicker, and the Spectrum component APIs remain unchanged. A type regression test covers spreading form-style onFocus and onBlur handlers that target HTMLElement into DateRangePicker.

This change was developed with assistance from Codex. I reviewed and understand every change and
remain responsible for this contribution.

✅ 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). A TypeScript regression test was added; Storybook is not applicable because this is a type-only change.
• Filled out test instructions.
• Updated documentation (if it already exists for this component). No documentation changes are needed because the default API and runtime behavior are unchanged.
• Looked at the Accessibility Practices for this feature - Aria Practices. Accessibility behavior is unchanged because this only refines TypeScript event target types.
• 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.

📝 Test Instructions:

1. Run yarn check-types.
2. Verify that a DateRangePickerProps<DateValue, HTMLElement> object with onFocus and onBlur
   handlers typed as React.FocusEvent<HTMLElement> can be spread into <DateRangePicker />.
3. Run the React Aria Components DateRangePicker and React Aria date picker Jest suites.

Automated checks run locally:

• corepack yarn check-types
• corepack yarn oxfmt --check on the five changed files
• corepack yarn oxlint on the five changed files
• corepack yarn test packages/react-aria-components/test/DateRangePicker.test.js packages/react-aria/test/datepicker/useDatePicker.test.tsx --runInBand (17 tests passed)

🧢 Your Project:

Personal/open-source contribution.