replace source links with API doc links /4/m2

Author: Rick-Anderson

aspnetcore/fundamentals/error-handling.md

@@ -81,9 +81,9 @@ Another way to use a lambda is to set the status code based on the exception typ
 
 ## IExceptionHandler
 
-[IExceptionHandler](https://source.dot.net/#Microsoft.AspNetCore.Diagnostics/ExceptionHandler/IExceptionHandler.cs,adae2915ad0c6dc5) is an interface that gives the developer a callback for handling known exceptions in a central location.
+[IExceptionHandler](/dotnet/api/microsoft.aspnetcore.diagnostics.iexceptionhandler) is an interface that gives the developer a callback for handling known exceptions in a central location.
 
-`IExceptionHandler` implementations are registered by calling [`IServiceCollection.AddExceptionHandler<T>`](https://source.dot.net/#Microsoft.AspNetCore.Diagnostics/ExceptionHandler/ExceptionHandlerServiceCollectionExtensions.cs,e74aac24e3e2cbc9). The lifetime of an `IExceptionHandler` instance is singleton. Multiple implementations can be added, and they're called in the order registered.
+`IExceptionHandler` implementations are registered by calling [`IServiceCollection.AddExceptionHandler<T>`](/dotnet/api/microsoft.extensions.dependencyinjection.exceptionhandlerservicecollectionextensions.addexceptionhandler) [`IServiceCollection.AddExceptionHandler<T>`](https://source.dot.net/#Microsoft.AspNetCore.Diagnostics/ExceptionHandler/ExceptionHandlerServiceCollectionExtensions.cs,e74aac24e3e2cbc9). The lifetime of an `IExceptionHandler` instance is singleton. Multiple implementations can be added, and they're called in the order registered.
 
 If an exception handler handles a request, it can return `true` to stop processing. If an exception isn't handled by any exception handler, then control falls back to the default behavior and options from the middleware. Different metrics and logs are emitted for handled versus unhandled exceptions.