[expo-av] allow playing media files from apk res folder (expo#8936)

# Why

ref expo#8888 -- expo-av currently does not support playing media files from an android apk's `res/raw` folder, which is where the RN packager embeds required assets by default.

# How

RN's asset source resolver sets the `uri` for assets embedded in `res` to simply the resource name with no scheme. Therefore, if the url provided to expo-av has no scheme, we can assume it comes from RN's asset source resolver and is a resource name. ([We do the same thing in expo-file-system.](https://github.com/expo/expo/blob/1b61af26782c89da45ba559e60ebb2a38b6e80b3/packages/expo-file-system/android/src/main/java/expo/modules/filesystem/FileSystemModule.java#L312-L314))

# Test Plan

Tested using the repo provided in expo#8888 and confirmed that with expo-updates disabled, after this change, the audio file played as expected both with ExoPlayer and with `androidImplementation: 'MediaPlayer'`.

packages/expo-av/CHANGELOG.md

@@ -11,6 +11,8 @@
 
 ### 🐛 Bug fixes
 
+- Allow playing media files embedded as resources in an Android APK. ([#8936](https://github.com/expo/expo/pull/8936) by [@esamelson](https://github.com/esamelson))
+
 ## 8.2.1 — 2020-05-29
 
 _This version does not introduce any user-facing changes._

packages/expo-av/android/src/main/java/expo/modules/av/player/MediaPlayerData.java

@@ -69,8 +69,13 @@ public void load(final Bundle status,
     final MediaPlayer unpreparedPlayer = new MediaPlayer();
 
     try {
+      Uri uri = mUri;
+      if (uri.getScheme() == null) {
+        int resourceId = mAVModule.getContext().getResources().getIdentifier(uri.toString(), "raw", mAVModule.getContext().getPackageName());
+        uri = Uri.parse("android.resource://" + mAVModule.getContext().getPackageName() + "/" + resourceId);
+      }
       if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
-        unpreparedPlayer.setDataSource(mAVModule.getContext(), mUri, null, getHttpCookiesList());
+        unpreparedPlayer.setDataSource(mAVModule.getContext(), uri, null, getHttpCookiesList());
       } else {
         Map<String, String> headers = new HashMap<>(1);
         StringBuilder cookieBuilder = new StringBuilder();
@@ -89,7 +94,7 @@ public void load(final Bundle status,
             }
           }
         }
-        unpreparedPlayer.setDataSource(mAVModule.getContext(), mUri, headers);
+        unpreparedPlayer.setDataSource(mAVModule.getContext(), uri, headers);
       }
     } catch (final Throwable throwable) {
       loadCompletionListener.onLoadError("Load encountered an error: setDataSource() threw an exception was thrown with message: " + throwable.toString());

packages/expo-av/android/src/main/java/expo/modules/av/player/SimpleExoPlayerData.java

@@ -8,6 +8,7 @@
 import androidx.annotation.Nullable;
 
 import android.text.TextUtils;
+import android.util.Log;
 import android.util.Pair;
 import android.view.Surface;
 
@@ -40,6 +41,7 @@
 import com.google.android.exoplayer2.upstream.DataSource;
 import com.google.android.exoplayer2.upstream.DataSpec;
 import com.google.android.exoplayer2.upstream.DefaultBandwidthMeter;
+import com.google.android.exoplayer2.upstream.RawResourceDataSource;
 import com.google.android.exoplayer2.util.Util;
 
 import java.io.IOException;
@@ -54,6 +56,7 @@ class SimpleExoPlayerData extends PlayerData
   implements Player.EventListener, ExtractorMediaSource.EventListener, SimpleExoPlayer.VideoListener, AdaptiveMediaSourceEventListener {
 
   private static final String IMPLEMENTATION_NAME = "SimpleExoPlayer";
+  private static final String TAG = SimpleExoPlayerData.class.getSimpleName();
 
   private SimpleExoPlayer mSimpleExoPlayer = null;
   private String mOverridingExtension;
@@ -367,6 +370,17 @@ public void onRenderedFirstFrame() {
 
   // https://github.com/google/ExoPlayer/blob/2b20780482a9c6b07416bcbf4de829532859d10a/demos/main/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java#L365-L393
   private MediaSource buildMediaSource(Uri uri, String overrideExtension, Handler mainHandler, DataSource.Factory factory) {
+    try {
+      if (uri.getScheme() == null) {
+        int resourceId = mReactContext.getResources().getIdentifier(uri.toString(), "raw", mReactContext.getPackageName());
+        DataSpec dataSpec = new DataSpec(RawResourceDataSource.buildRawResourceUri(resourceId));
+        final RawResourceDataSource rawResourceDataSource = new RawResourceDataSource(mReactContext);
+        rawResourceDataSource.open(dataSpec);
+        uri = rawResourceDataSource.getUri();
+      }
+    } catch (Exception e) {
+      Log.e(TAG, "Error reading raw resource from ExoPlayer", e);
+    }
     @C.ContentType int type = TextUtils.isEmpty(overrideExtension) ? Util.inferContentType(String.valueOf(uri)) : Util.inferContentType("." + overrideExtension);
     switch (type) {
       case C.TYPE_SS: