Fix/all touch and perf fixes

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Greptile Summary

This PR consolidates a broad set of touch correctness fixes and performance improvements across the Windows Composition layer. Key behavioural fixes include: stale-pointer cancellation on repeated press (replacing a silent early-return), correct pointer-device-type detection (Touch/Pen/Mouse), proper screenPoint assignment in UpdateActiveTouch, an altDown key check that was querying the Control key instead of Menu/Alt, a duplicate altKey guard in the submit-key condition, and a hover-out timer stored in the wrong field (_hoverInDelayTimeout). Performance improvements include m_childrenCache for O(1) child lookup, vector → unordered_set for captured pointers / component names / animated-node children, and an O(n²)→O(n) rewrite of anyHitTestHelper. Thread safety is tightened with std::call_once for DLL loading and std::atomic<bool> for m_usingRendering.

Confidence Score: 5/5

PR is safe to merge; all findings are confirmations of intentional bug fixes, with no new defects introduced.

All inline comments describe fixes rather than new bugs. The comments left are P2 observations confirming that the fixes are correct. No regressions found across the C++ or JS changes.

CompositionEventHandler.cpp deserves a manual touch-flow smoke-test given the scope of the stale-pointer cancellation logic.

Important Files Changed

Filename	Overview
vnext/Microsoft.ReactNative/Fabric/Composition/CompositionEventHandler.cpp	Major touch-handling overhaul: stale-pointer cancellation, correct device-type detection (Touch/Pen/Mouse), screenPoint fix, unordered_set for captured pointers, null-safe RootComponentView, PointerExited revoker, and new DispatchSynthesizedTouchCancelForActiveTouch helper.
vnext/Microsoft.ReactNative/Fabric/Composition/CompositionContextHelper.cpp	Added m_childrenCache vector for O(1) GetAt; fixed InsertAt to maintain cache on both code paths; added snap-position change detection to avoid redundant InteractionTracker reconfiguration.
vnext/Microsoft.ReactNative/Fabric/Composition/TextInput/WindowsTextInputComponentView.cpp	Added destructor, CompTextHost::Detach(), and m_outer null-guards throughout to prevent UAF; std::call_once for DLL load; touch messages now mapped to WM_LBUTTONDOWN/WM_LBUTTONDBLCLK/WM_MOUSEMOVE; altDown key and duplicate altKey guard fixed; OnTxSetCursor moved inside m_textServices guard.
vnext/Microsoft.ReactNative/Fabric/Composition/CompositionViewComponentView.cpp	anyHitTestHelper now snapshots children into a local vector to avoid O(n²) IVector::GetAt access pattern; semantics and reverse-iteration order preserved.
vnext/src-win/Libraries/Pressability/Pressability.windows.js	Two fixes: hoverOut timer correctly stored in _hoverOutDelayTimeout (was _hoverInDelayTimeout); disabled check simplified to disabled !== true.
vnext/src-win/Libraries/Components/View/View.windows.js	tabIndex focusable logic fixed: !tabIndex (treated positive tabIndex as non-focusable) replaced with tabIndex >= 0 (correct HTML semantics).
vnext/Microsoft.ReactNative/Modules/Timing.h	m_usingRendering changed to std::atomic to eliminate a data race between the UI thread and the rendering callback.

Sequence Diagram

sequenceDiagram
    participant OS as OS Pointer Source
    participant CEH as CompositionEventHandler
    participant AT as m_activeTouches
    participant EE as EventEmitter (JS)

    OS->>CEH: onPointerPressed(pointerId)
    CEH->>AT: find(pointerId)
    alt stale touch found
        AT-->>CEH: staleTouch
        CEH->>EE: DispatchSynthesizedTouchCancel(staleTouch)
        CEH->>AT: erase(pointerId)
    end
    CEH->>AT: insert new ActiveTouch (Touch/Pen/Mouse type)
    CEH->>EE: onTouchStart / onPointerDown

    OS->>CEH: onPointerReleased(pointerId)
    CEH->>AT: find(pointerId)
    alt tag == -1 (pointer left surface)
        CEH->>EE: DispatchSynthesizedTouchCancel
        CEH->>AT: erase(pointerId)
    else normal release
        CEH->>EE: onTouchEnd / onPointerUp
        CEH->>AT: erase(pointerId)
    end

    OS->>CEH: onPointerCaptureLost
    CEH->>AT: releasePointerCapture (unordered_set.erase)

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