fix(DropdownMenu): light-dismiss + click-toggle race on touch browsers

[lexs]

Summary

On iOS Safari (and other touch browsers where pointerdown fires light-dismiss before the trigger's click event), tapping the XDSDropdownMenu trigger to close an open menu would close and then immediately re-open on the same tap. The hide flows through useXDSPopover's onHide first, then the click hits handleButtonClick, which reads popover.isOpen=false and toggles it back to true.

Mirror the existing 50ms hide-time guard in XDSPopover (lines 268, 274–277, 290–296 — same race, same fix) into XDSDropdownMenu: stamp lastHideTimeRef in handleLayerHide, then short-circuit handleButtonClick if it fires within 50ms of that stamp.

Also fixes XDSMoreMenu since it wraps XDSDropdownMenu.

This ports the equivalent internal fix (Meta D104032592 in fbsource, which patches XDSInternalPopoverMenu.react.js — the shared internal layer behind both XDSDropdownMenu and XDSPopoverMenu) to the public xds repo. Here, the internal layer is useXDSPopover, but XDSDropdownMenu calls into it directly with its own toggle logic, so the guard goes alongside that logic. XDSPopover already has the equivalent guard for the same race.

Test Plan

Added a regression test in XDSDropdownMenu.test.tsx that fires open → close → click and asserts the menu does not re-open (showPopover/hidePopover each called exactly once).

$ yarn test packages/core/src/DropdownMenu/XDSDropdownMenu.test.tsx
 Test Files  1 passed (1)
      Tests  29 passed (29)

$ yarn test packages/core/src/Popover/XDSPopover.test.tsx packages/core/src/MoreMenu/XDSMoreMenu.test.tsx
 Test Files  2 passed (2)
      Tests  31 passed (31)

$ yarn workspace @xds/core build
✅ Build success

ESLint clean on the changed files (one pre-existing unused-container warning in an unrelated test left as-is).

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[github-actions]

PR Analysis Report

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No new or modified components detected.

Bundle Size Summary

Package	Size (ESM)	Size (CJS)	Gzipped
@xds/core	18.3KB	28.3KB	4.2KB

Accessibility Audit

Status: No accessibility violations detected.

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[cixzhang]

Clean fix. Timestamp guard is the right approach for the iOS event ordering race. Minimal, well-tested, no regression risk.