Fix: change exceptions to have meaningful directions to documentation to help users. (#1616)

The ones that are used for different nuget packages to indicate to the user they need to add a nuget package to their project due to the lack of DI registration.

Author: ghuntley

src/ReactiveUI/Platforms/netstandard2.0/PlatformRegistrations.cs

@@ -10,7 +10,7 @@ public class PlatformRegistrations : IWantsToRegisterStuff
     {
         public void Register(Action<Func<object>, Type> registerFunction)
         {
-            throw new Exception("You are referencing the Portable version of ReactiveUI in an App. Reference the platform-specific version.");
+            throw new Exception("You are referencing the Portable version of ReactiveUI in an App. Please change your reference to the specific version for your platform found here: https://reactiveui.net/docs/getting-started/installation/nuget-packages");
         }
     }
 }

src/ReactiveUI/Platforms/windows-common/RoutedViewHost.cs

@@ -76,8 +76,8 @@ public RoutedViewHost()
 
             if (platform == null) {
                 // NB: This used to be an error but WPF design mode can't read
-                // good or do other stuff good.
-                this.Log().Error("Couldn't find an IPlatformOperations. This should never happen, your dependency resolver is broken");
+                // good or do other stuff good.                
+                this.Log().Error("Couldn't find an IPlatformOperations implementation. Please make sure you have installed the latest version of the ReactiveUI packages for your platform. See https://reactiveui.net/docs/getting-started/installation/nuget-packages for guidance.");
             } else {
                 platformGetter = () => platform.GetOrientation();
             }

src/ReactiveUI/Platforms/windows-common/ViewModelViewHost.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
@@ -87,7 +87,7 @@ public ViewModelViewHost()
             if (platform == null) {
                 // NB: This used to be an error but WPF design mode can't read
                 // good or do other stuff good.
-                this.Log().Error("Couldn't find an IPlatformOperations. This should never happen, your dependency resolver is broken");
+                this.Log().Error("Couldn't find an IPlatformOperations implementation. Please make sure you have installed the latest version of the ReactiveUI packages for your platform. See https://reactiveui.net/docs/getting-started/installation/nuget-packages for guidance.");
             } else {
                 platformGetter = () => platform.GetOrientation();
             }

src/ReactiveUI/ReactiveNotifyPropertyChangedMixin.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
@@ -173,8 +173,7 @@ static IObservable<IObservedChange<object, object>> notifyForProperty(object sen
             }
 
             if (result == null) {
-                throw new Exception(
-                    String.Format($"Couldn't find a ICreatesObservableForProperty for {sender.GetType()} property {propertyName}. This should never happen, your service locator is probably broken."));
+                throw new Exception($"Could not find a ICreatesObservableForProperty for {sender.GetType()} property {propertyName}. This should never happen, your service locator is probably broken. Please make sure you have installed the latest version of the ReactiveUI packages for your platform. See https://reactiveui.net/docs/getting-started/installation/nuget-packages for guidance.");
             }
 
             return result.GetNotificationForProperty(sender, expression, propertyName, beforeChange);