feat: ios native anr capture

[bitsandfoxes]

Resolves https://github.com/getsentry/team-gdx/issues/151

What does it do

This PR forwards the new flag EnableAppHangTracking to sentry-cocoa (maps to enableAppHangTracking). The timeout is reused. This replaces the C# watchdog on platforms that are supported by sentry-cocoa.

Why does it do it

On iOS, the Unity player loop runs on the main thread (the one with the CFRunLoop). The generated UnityAppController.mm registers Unity's frame tick as a CADisplayLink callback on the main run loop. Every Update, FixedUpdate, and LateUpdate execute on that single thread. Native UIKit/AppKit events share the same queue.
So when a Unity script blocks (e.g. infinite loop in Update, synchronous I/O, deadlock on .Wait()), it blocks the iOS main run loop directly. sentry-cocoa's watchdog enqueues a block on the main queue and times its execution. That means if Unity is stuck, that block never runs, and that hang is reported.

This allows us to replace the Unity SDK C# ANR integration. The generated native ANR event from sentry-cocoa contains an actual stack trace, making the report actually actionable.

How does it do it

We're in the process of deprecating AnrEnabled and putting the app freeze capture behaviour under EnableAppHangTracking. But unlike on Android, this replaces the C# watchdog entirely. We will need to follow up on this for Android as well, see #2681

Result

The resulting native event contains a fully symbolicated stack trace of the C# code that caused the freeze.

Follow up

We'll need to work on the in-app frames to clean up the stack trace presentation.

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