Mobile: User.Other is included in managed errors but not native ones

[bruno-garcia]

When using the SDK's C# API to change the Scope, we're able to pass down some fields to the native layer.
So if a crash is caused by Java/Kotlin/Objective-C/Swift/C/C++ etc, it'll include User top level firleds and tags.

How it works: Setting the user in C# triggers the ScopeObserver:

sentry-dotnet/src/Sentry/Scope.cs

Lines 120 to 139 in 5f0f087

	public SentryUser User
	{
	get => _user ??= new SentryUser
	{
	PropertyChanged = UserChanged
	};
	set
	{
	if (_user != value)
	{
	_user = value;
	if (_user is not null)
	{
	_user.PropertyChanged = UserChanged;
	}
	UserChanged.Invoke(_user);
	}
	}
	}

So on iOS for example, we'll set the user as such:

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

Lines 92 to 103 in 5f0f087

	public void SetUser(SentryUser? user)
	{
	try
	{
	var u = user?.ToCocoaUser();
	SentryCocoaSdk.ConfigureScope(scope => scope.SetUser(u));
	}
	finally
	{
	_innerObserver?.SetUser(user);
	}
	}

On Android:

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

Lines 90 to 100 in 5f0f087

	public void SetUser(SentryUser? user)
	{
	try
	{
	var u = user?.ToJavaUser();
	JavaSdk.Sentry.SetUser(u);
	}
	finally
	{
	_innerObserver?.SetUser(user);
	}

And Native ([sentry-native](https://github.com/getsentry/sentry-native)):

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

Lines 30 to 39 in 5f0f087

	public override void SetUserImpl(SentryUser user)
	{
	// see https://develop.sentry.dev/sdk/event-payloads/user/
	var cUser = C.sentry_value_new_object();
	C.SetValueIfNotNull(cUser, "id", user.Id);
	C.SetValueIfNotNull(cUser, "username", user.Username);
	C.SetValueIfNotNull(cUser, "email", user.Email);
	C.SetValueIfNotNull(cUser, "ip_address", user.IpAddress);
	C.sentry_set_user(cUser);
	}

But we don't include everything, and that's not documented anywhere it seems.

For example, we don't sync down to native User.Other. And this can be a pitfall to customers.
We need to at least clearly document this, or expand scope sync for this field.

[bruno-garcia]

came from a customer, cc @JLuse ^

[bitsandfoxes]

Documenting the pitfall won't fix bad UX. And looking at what sentry-native allows us to do we should sync down Other.
Don't hang me for my native code but something like this should work:

sentry_value_t user = sentry_value_new_object();
sentry_value_t other = sentry_value_new_object()
sentry_value_set_by_key(other, "my_key", sentry_value_new_string("my_value"));
// add all the stuff
sentry_value_set_by_key(user, "contexts", other);

sentry_set_user(user);