Recognize "SMPL" files as playlists.

The file format isn't well-documented, so we can't parse it, but at
least we can make it visible to Music player apps.

Bug: 143707020
Test: atest --test-mapping packages/providers/MediaProvider
Change-Id: I20047331fb4c0ff81d1fc16ed543c542254467e3
diff --git a/src/com/android/providers/media/util/MimeUtils.java b/src/com/android/providers/media/util/MimeUtils.java
index cf2f6e2..bb376d0 100644
--- a/src/com/android/providers/media/util/MimeUtils.java
+++ b/src/com/android/providers/media/util/MimeUtils.java
@@ -91,6 +91,7 @@
         switch (mimeType) {
             case "application/vnd.apple.mpegurl":
             case "application/vnd.ms-wpl":
+            case "application/x-extension-smpl":
             case "application/x-mpegurl":
             case "audio/mpegurl":
             case "audio/x-mpegurl":