[No-QA] refactor: introduce shared Overlay primitives

[TaduJR]

Explanation of Change

M1 of a five-PR split of the Modal v2 / Dialog / Popover v2 / PopoverMenu v2 decomposition. This PR ships the shared bottom layer — a new Overlay/ primitive folder plus a few small cross-feature hooks/libs — that the next four PRs compose on. No consumer migration here; every existing user-facing surface is byte-identical to main.

Contents:

• src/components/Overlay/: DismissableLayer, FloatingHost, Portal, Presence, AnimatedSurface, createHeadingSystem, plus 12 hooks (Esc handling, anchored positioning, aria-hide, body-scroll lock, focus management, etc.) and 7 libs (anchor measurement, dismissable-layer stack store, external-store factory, etc.)
• Cross-feature hooks: useCallbackRef, useControlledState, useDisclosureState
• Cross-feature libs: composeEventHandlers, isHTMLElement
• Non-breaking widening: FocusTrapForModal.shouldReturnFocus accepts () => boolean so M2 can resolve the Composer-focus baton at restore time
• Re-exports PressableRefElement from Pressable/GenericPressable/types.ts so M1's measureAnchor / overlayStore can type their anchor refs
• 2 CONST entries (OVERLAY_FADE_IN_WEB / OVERLAY_FADE_OUT_WEB), 1 style (overlayPortalHost)

Fixed Issues

$ #91238
PROPOSAL:

Tests

• Verify that no errors appear in the JS console

Offline tests

QA Steps

// TODO: These must be filled out, or the issue title must include "[No QA]."
Same as tests

• Verify that no errors appear in the JS console

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
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Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

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Codecov Report

✅ Changes either increased or maintained existing code coverage, great job!

Files with missing lines	Coverage Δ
src/CONST/index.ts	93.84% <ø> (ø)
...ents/Overlay/DismissableLayer/LayerDepthContext.ts	100.00% <100.00%> (ø)
src/components/Overlay/FloatingHost.tsx	100.00% <100.00%> (ø)
src/components/Overlay/Portal/index.tsx	100.00% <100.00%> (ø)
src/components/Overlay/PortalContext.ts	100.00% <100.00%> (ø)
...nts/Overlay/hooks/useAnchoredPosition/index.web.ts	100.00% <100.00%> (ø)
...ents/Overlay/hooks/useDismissOnAnchorMove/index.ts	100.00% <100.00%> (ø)
src/components/Overlay/hooks/useHeadingState.ts	100.00% <100.00%> (ø)
src/components/Overlay/hooks/useOverlayEntry.ts	100.00% <100.00%> (ø)
src/components/Overlay/hooks/useOverlayTrigger.ts	100.00% <100.00%> (ø)
... and 33 more
... and 32 files with indirect coverage changes

[TaduJR]

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[linhvovan29546]

@TaduJR This PR introduce ~4000 lines of new code have no production consumer — nothing in Modal, Popover, or PopoverMenu imports from it. The unit tests verify internal logic, but real integration (focus, navigation, Onyx state) is untested until M2-M5. Could we include at least one thin integration proof (e.g., migrating a single popover to FloatingHost) to validate the foundation end-to-end before building on top of it? cc @roryabraham, what are your thoughts?