Add in-process hang tracking with Native backend on Windows, Linux, and Mac

[tustanivsky]

This PR adds opt-in native app-hang detection powered by sentry-native alongside the existing engine FThreadHeartBeat hang watcher.

• Example hang event captured on Windows
• Example hang event captured on Linux
• Example hang event captured on Mac

Key changes

• Added a new UseNativeHangTracking setting under Hang Tracking (requires EnableHangTracking). When enabled, hangs are detected by sentry-native's in-process app-hang watchdog instead of Unreal Engine's FThreadHeartBeat watcher.
• Configures sentry_options_set_enable_app_hang_tracking and sentry_options_set_app_hang_timeout before sentry_init, reusing the existing HangTimeoutDuration value.
• Registers a per-frame heartbeat on FCoreDelegates::OnEndFrame. The first tick marks the game thread as monitored, and subsequent frames refresh the heartbeat via sentry_app_hang_heartbeat.
• When the heartbeat becomes stale, the watchdog thread captures an App Hang event while the application continues running.
• The engine-based FSentryHangWatcher remains the default implementation and is disabled only when UseNativeHangTracking is enabled, preventing duplicate hang reports.

Testing

• Desktop integration tests are data-driven over the two mechanisms (Engine/Native), gated per platform/backend (macOS runs the Native mechanism under the Native backend).

Known limitations

• Desktop only (Windows/Linux/macOS). On mobile, the platform SDKs' built-in ANR/App Hang detection applies.

Documentation

• docs(unreal): opt-in native app-hang tracking on desktop platforms sentry-docs#18534

Relate items

• feat(native): Added App Hang capture for Windows sentry-native#1781
• feat(native): Added App Hang capture for Linux sentry-native#1801
• feat(native): Added App Hang capture for macOS sentry-native#1780
• Add app hang tracking for Windows and Linux #1270
• feat: in proc App Hang capture sentry-native#1806

[github-actions]

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[bitsandfoxes]

I wonder whether we should keep this as experimental and opt-in for a bit? The new bits and pieces in sentry-native suspend the main thread, so some real-life validation before enabling this by default would be nice.

That's also the way I intend to do it for Unity: getsentry/sentry-unity#2709

[tustanivsky]

I wonder whether we should keep this as experimental and opt-in for a bit?

@bitsandfoxes Yes, it makes sense to add this as an opt-in feature. By default, the SDK continues to use Unreal's hang watcher (FThreadHeartBeat / FSentryHangWatcher) while the native's hang tracking is only enabled when configured explicitly.