Propagate `Trace ID` to native layer

[bitsandfoxes]

Context

With #4026 the SDK now accepts SetTrace from other "Head SDKs" like the Unity SDK. This builds on top of TwP and allows them to directly set the PropagationContext without having to go through the ContinueTrace.

With this change we've also extended the IScopeObserver to observe changes to the PropagationContext and pass then on to the native layer.

Goals

The goal is to have the .NET SDK pass on the trace ID to the native SDK via the respective ScopeObserver.

Native ✅

Platforms that are covered by sentry-native got this functionality with #4026 and the observer observes.

sentry-dotnet/src/Sentry/Platforms/Native/NativeScopeObserver.cs

Lines 43 to 44 in 438ae83

	public override void SetTraceImpl(SentryId traceId, SpanId parentSpanId) =>
	C.sentry_set_trace(traceId.ToString(), parentSpanId.ToString());

Android

Supporting this on Android is currently blocked by #3911. The feature requires at least 8.4.0.

sentry-dotnet/src/Sentry/Platforms/Android/AndroidScopeObserver.cs

Lines 103 to 106 in 438ae83

	public void SetTrace(SentryId traceId, SpanId parentSpanId)
	{
	// TODO: This requires sentry-java 8.4.0
	}

Cocoa

The Cocoa SDK is missing the functionality to have the trace ID passed. Once that's done we'll need to update the CocoaScopeObserver

sentry-dotnet/src/Sentry/Platforms/Cocoa/CocoaScopeObserver.cs

Lines 111 to 114 in 438ae83

	public void SetTrace(SentryId traceId, SpanId parentSpanId)
	{
	// TODO: Missing corresponding functionality on the Cocoa SDK
	}