Fix ToastContentBuilder audio ms-winsoundevent and ms-appx (#3755)

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## Fixes #3753
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Add support for using ms-windsoundevent and ms-appx in the toast content audio builder (previously we were incorrectly throwing an exception when devs provided those). Also added unit tests to ensure this works correctly and ensure we correctly throw on https audio urls and other non-supported ones.

## PR Type
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- Bugfix
<!-- - Feature -->
<!-- - Code style update (formatting) -->
<!-- - Refactoring (no functional changes, no api changes) -->
<!-- - Build or CI related changes -->
<!-- - Documentation content changes -->
<!-- - Sample app changes -->
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## What is the current behavior?
<!-- Please describe the current behavior that you are modifying, or link to a relevant issue. -->

Throws when you try to use `ms-winsoundevent:` or `ms-appx:`, both of which are supported by Windows. Today it only supports absolute file paths (`C:\audio.mp3`), which are only supported by desktop apps.


## What is the new behavior?
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Doesn't throw for those.


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## Other information

Author: msftbot[bot]

Microsoft.Toolkit.Uwp.Notifications/Toasts/Builder/ToastContentBuilder.cs

@@ -355,25 +355,20 @@ public ToastContentBuilder AddAudio(
             bool? silent = default)
 #endif
         {
-            if (!src.IsFile)
-            {
-                throw new ArgumentException(nameof(src), "Audio Source has to be a file.");
-            }
-
-            Content.Audio = new ToastAudio();
-            Content.Audio.Src = src;
+            var audio = new ToastAudio();
+            audio.Src = src;
 
             if (loop != default)
             {
-                Content.Audio.Loop = loop.Value;
+                audio.Loop = loop.Value;
             }
 
             if (silent != default)
             {
-                Content.Audio.Silent = silent.Value;
+                audio.Silent = silent.Value;
             }
 
-            return this;
+            return AddAudio(audio);
         }
 
         /// <summary>
@@ -383,6 +378,11 @@ public ToastContentBuilder AddAudio(
         /// <returns>The current instance of <see cref="ToastContentBuilder"/></returns>
         public ToastContentBuilder AddAudio(ToastAudio audio)
         {
+            if (audio.Src != null && !audio.Src.IsFile && audio.Src.Scheme != "ms-appx" && audio.Src.Scheme != "ms-winsoundevent")
+            {
+                throw new InvalidOperationException("Audio Source must either be a ms-appx file, absolute file, or ms-winsoundevent.");
+            }
+
             Content.Audio = audio;
             return this;
         }

UnitTests/UnitTests.Notifications.Shared/TestToastContentBuilder.cs

@@ -548,6 +548,72 @@ public void AddAudioTest_WithFullArgs_ReturnSelfWithCustomAudioAddedWithAllOptio
             Assert.AreEqual(testToastAudioSilent, builder.Content.Audio.Silent);
         }
 
+        [TestMethod]
+        public void AddAudioTest_WithMsWinSoundEvent_ReturnSelfWithCustomAudioAdded()
+        {
+            // Arrange
+            Uri testAudioUriSrc = new Uri("ms-winsoundevent:Notification.Reminder");
+
+            // Act
+            ToastContentBuilder builder = new ToastContentBuilder();
+            ToastContentBuilder anotherReference = builder.AddAudio(testAudioUriSrc);
+
+            // Assert
+            Assert.AreSame(builder, anotherReference);
+            Assert.AreEqual(testAudioUriSrc.OriginalString, builder.Content.Audio.Src.OriginalString);
+        }
+
+        [TestMethod]
+        public void AddAudioTest_WithMsAppx_ReturnSelfWithCustomAudioAdded()
+        {
+            // Arrange
+            Uri testAudioUriSrc = new Uri("ms-appx:///Assets/Audio.mp3");
+
+            // Act
+            ToastContentBuilder builder = new ToastContentBuilder();
+            ToastContentBuilder anotherReference = builder.AddAudio(testAudioUriSrc);
+
+            // Assert
+            Assert.AreSame(builder, anotherReference);
+            Assert.AreEqual(testAudioUriSrc.OriginalString, builder.Content.Audio.Src.OriginalString);
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(InvalidOperationException))]
+        public void AddAudioTest_WithInvalidMsUri_ThrowException()
+        {
+            // Arrange
+            Uri testAudioUriSrc = new Uri("ms-doesntexist:Notification.Reminder");
+
+            // Act
+            ToastContentBuilder builder = new ToastContentBuilder();
+            builder.AddAudio(testAudioUriSrc);
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(InvalidOperationException))]
+        public void AddAudioTest_WithInvalidAppDataUri_ThrowException()
+        {
+            // Arrange (ms-appdata isn't currently supported)
+            Uri testAudioUriSrc = new Uri("ms-appdata:///local/Sound.mp3");
+
+            // Act
+            ToastContentBuilder builder = new ToastContentBuilder();
+            builder.AddAudio(testAudioUriSrc);
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(InvalidOperationException))]
+        public void AddAudioTest_WithInvalidHttpUri_ThrowException()
+        {
+            // Arrange
+            Uri testAudioUriSrc = new Uri("https://myaudio.com/song.mp3");
+
+            // Act
+            ToastContentBuilder builder = new ToastContentBuilder();
+            builder.AddAudio(testAudioUriSrc);
+        }
+
         [TestMethod]
         public void AddAudioTest_WithAudioObject_ReturnSelfWithCustomAudioAdded()
         {