fix(AppLifecycle): deduplicate file activations from multi-process Shell launches

[MuyuanMS]

fix(AppLifecycle): Deduplicate file activations from multi-process Shell launches\n\n## Problem\n\nWhen a user selects multiple files in Windows Explorer and opens them with a packaged Win32 app using the Windows App SDK single-instance pattern (FindOrRegisterForKey), the app receives N separate Activated events (one per file), each containing all N files.\n\nThis happens because:\n1. Shell behavior: For Win32 packaged apps, the Shell launches N separate processes (one per file)\n2. Platform API: Each process's GetActivatedEventArgs() returns the full set of N files\n3. Single-instance redirection: All N processes redirect to the key owner with identical activation args\n4. Result: N × N redundancy — N identical activations, each with all N files\n\nIn UWP, the Shell batched files into a single activation. This regression was reported in #5066.\n\n## Solution\n\nAdd a fingerprint-based deduplication mechanism in AppInstance that suppresses redundant file activations:\n\n1. ComputeFileActivationFingerprint() — Computes a size_t hash from the activation verb + file paths. Returns 0 for non-file activations (no dedup applied).\n\n2. IsDuplicateFileActivation() — Checks if a fingerprint matches the last seen fingerprint within a 2-second window. Uses SRWLOCK for thread safety between the main thread and the activation watcher threadpool.\n\n3. GetActivatedEventArgs() — Records the initial activation fingerprint for the current instance, so that subsequent identical redirected activations are recognized as duplicates.\n\n4. ProcessRedirectionRequests() — Checks each redirected activation against the dedup table before firing the Activated event. Always signals the cleanup event so redirecting processes can exit cleanly.\n\n## Design Decisions\n\n- 2-second dedup window: All N processes launch within milliseconds of each other, so 2 seconds is more than sufficient. Short enough to allow legitimate repeated activations.\n- Hash-based fingerprint: Uses std::hash<std::wstring> (available via <string> in pch.h) for compact storage. No additional STL includes needed.\n- SRWLOCK: Lightweight in-process synchronization, consistent with Win32 primitives used elsewhere in the codebase.\n- Best-effort: If fingerprinting fails (e.g., QI fails on COM-proxied activation data), the code falls back to delivering the activation (no regression).\n- Non-file activations unaffected: Only ExtendedActivationKind::File activations are deduplicated.\n\n## Files Changed\n\n| File | Change |\n|------|--------|\n| dev/AppLifecycle/AppInstance.h | Add dedup members (SRWLOCK, fingerprint, timestamp) and method declarations |\n| dev/AppLifecycle/AppInstance.cpp | Implement ComputeFileActivationFingerprint(), IsDuplicateFileActivation(), modify GetActivatedEventArgs() and ProcessRedirectionRequests() |\n| dev/AppLifecycle/FileActivatedEventArgs.h | Revert to original single-file constructor (remove unused multi-file constructor) |\n\n## Testing\n\n- Build verified: BuildAll.ps1 -Platform x64 -Configuration Release → exit code 0\n- Manual test scenario: Select 5+ files in Explorer → Open with single-instance packaged app → Should receive 1 activation instead of 5\n\nFixes #5066"