Fix error message display for InAppNotification used in Sample App (#4061)

We missed updating a template somewhere, so fatal errors aren't displaying in the Sample App. Ideally this message never appears, this is being surfaced from our issues with `ICommand` in the ListView samples. #4039

## PR Type
What kind of change does this PR introduce?
<!-- Please uncomment one or more that apply to this PR. -->

<!-- - Bugfix -->
<!-- - Feature -->
<!-- - Code style update (formatting) -->
<!-- - Refactoring (no functional changes, no api changes) -->
<!-- - Build or CI related changes -->
<!-- - Documentation content changes -->
- Sample app changes
<!-- - Other... Please describe: -->


## What is the current behavior?
Error box appears blank.

## What is the new behavior?
Error message shows exception message.

## PR Checklist

Please check if your PR fulfills the following requirements:

- [ ] Tested code with current [supported SDKs](../readme.md#supported)
- [ ] Pull Request has been submitted to the documentation repository [instructions](..\contributing.md#docs). Link: <!-- docs PR link -->
- [ ] Sample in sample app has been added / updated (for bug fixes / features)
    - [ ] Icon has been created (if new sample) following the [Thumbnail Style Guide and templates](https://github.com/windows-toolkit/WindowsCommunityToolkit-design-assets)
- [ ] New major technical changes in the toolkit have or will be added to the [Wiki](https://github.com/windows-toolkit/WindowsCommunityToolkit/wiki) e.g. build changes, source generators, testing infrastructure, sample creation changes, etc...
- [ ] Tests for the changes have been added (for bug fixes / features) (if applicable)
- [ ] Header has been added to all new source files (run *build/UpdateHeaders.bat*)
- [ ] Contains **NO** breaking changes

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## Other information

Author: msftbot[bot]

Microsoft.Toolkit.Uwp.SampleApp/Pages/SampleController.xaml.cs

@@ -209,9 +209,9 @@ protected override async void OnNavigatedTo(NavigationEventArgs e)
                             method.Invoke(SamplePage, new object[] { e });
                         }
                     }
-                    catch
+                    catch (Exception ex)
                     {
-                        ExceptionNotification.Show("Sample Page failed to load.");
+                        ExceptionNotification.Show("Sample Page failed to load: " + ex.Message);
                     }
 
                     if (SamplePage != null)

Microsoft.Toolkit.Uwp.SampleApp/Styles/Generic.xaml

@@ -600,15 +600,18 @@
                                               Foreground="DarkRed"
                                               Glyph="" />
 
-                                    <ContentPresenter Grid.Column="1"
+                                    <ContentPresenter x:Name="PART_Presenter"
+                                                      Grid.Column="1"
                                                       HorizontalAlignment="{TemplateBinding HorizontalAlignment}"
-                                                      VerticalAlignment="Center"
+                                                      VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                                                       HorizontalContentAlignment="Stretch"
                                                       VerticalContentAlignment="Center"
+                                                      ContentTransitions="{TemplateBinding ContentTransitions}"
+                                                      FontWeight="SemiBold"
                                                       TextWrapping="WrapWholeWords" />
 
                                     <Button x:Name="PART_DismissButton"
-                                            Grid.Column="3"
+                                            Grid.Column="2"
                                             Margin="10,0,-10,0"
                                             AutomationProperties.Name="Dismiss"
                                             Content="&#xE894;"