feat: a11y: arrow key navigation support for list menu dropdown and select

[dkilgore-eightfold]

SUMMARY:

This change adds ArrowDown, ArrowLeft, ArrowRight, and ArrowUp keyboard navigation support to address existing usability bugs in List, Dropdown, Menu, CascadingMenu, and Select components.

• Moves SELECTOR string from useFocusTrap scope to utility scope so that it may be used by List
• Adds focusable function that returns true if certain attributes exist on element passed into it via args
• Adds arrow key support to List component via its new handleItemKeyDown function
• Updates List getItem prop implementation to be wrapped in externalItem so that we can access its properties
• Updates List getAdditionalItem such that it may be included in the focus loop
• Updates List to include an option to disable default arrow key handling via disableArrowKeys prop
• Updates Dropdown to support ArrowDown and ArrowUp keys via its handleReferenceKeyDown to open and close the Dropdown, when the Dropdown is open we place focus on the first focusable selector, when closed we place focus back on the reference element
• Adds new Dropdown story demonstrating additionalItem and renderAdditionalItem
• Adds initialFocus and referenceOnKeydown props to Dropdown
• Adds focusFirstElement and focusOnElement helpers to DropdownRef
• Exports DropdownRef via octuple.ts to assist with strict type implementations
• Updates Select to place focus back on its reference element when its Dropdown is closed
• Updates Select to include initialFocus prop to enable granular control of how its Dropdown steals focus
• Adds forwardRef support to MenuItemButton, MenuItemCustom, MenuItemLink, MenuItemSubHeader, and MenuItem components
• Updates MenuItemSubHeader to work with keyboard navigation, preserves current behavior
• Updates MenuProps, marking subHeader as deprecated because its not used
• Adds floating-ui useListNavigation support to CascadingMenu as its supported there by its canonical floating-ui implementation
• Updates related Button implementations to use variant prop
• Updates Stories
• Adds UTs

https://github.com/EightfoldAI/octuple/assets/99700808/55067a16-a82a-4cd5-af1f-f60bf8014bc7

GITHUB ISSUE (Open Source Contributors)

https://github.com/EightfoldAI/octuple/issues/757

JIRA TASK (Eightfold Employees Only):

ENG-72532 ENG-72534 ENG-72536

CHANGE TYPE:

• [ ] Bugfix Pull Request
• [x] Feature Pull Request

TEST COVERAGE:

• [ ] Tests for this change already exist
• [x] I have added unittests for this change

TEST PLAN:

Pull the PR branch and yarn and then yarn storybook. Verify the List, Dropdown, Menu, and Select stories behave as expected.

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[codecov[bot]]

Codecov Report

Attention: 40 lines in your changes are missing coverage. Please review.

Comparison is base (3791c41) 85.06% compared to head (a975b2a) 85.17%.

Files	Patch %	Lines
src/components/List/List.tsx	86.90%	11 Missing :warning:
src/components/Menu/CascadingMenu.tsx	79.59%	10 Missing :warning:
src/components/Dropdown/Dropdown.tsx	83.72%	7 Missing :warning:
...ts/Menu/MenuItem/MenuItemButton/MenuItemButton.tsx	90.47%	4 Missing :warning:
...onents/Menu/MenuItem/MenuItemLink/MenuItemLink.tsx	78.94%	4 Missing :warning:
src/components/Menu/Menu.tsx	0.00%	2 Missing :warning:
...ts/Menu/MenuItem/MenuItemCustom/MenuItemCustom.tsx	80.00%	1 Missing :warning:
src/components/Select/Select.tsx	96.42%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #759 +/- ## ========================================== + Coverage 85.06% 85.17% +0.10% ========================================== Files 908 908 Lines 18920 19113 +193 Branches 6987 7075 +88 ========================================== + Hits 16095 16279 +184 - Misses 2743 2752 +9 Partials 82 82 ```

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