build: enable r8 full mode

Enable R8 full mode for the app.

Should shave off ~150kb.

app/src/main/java/org/oxycblt/auxio/music/MusicRepository.kt

@@ -247,7 +247,8 @@ constructor(
             ?: userLibrary?.findPlaylist(uid))
 
     override fun createPlaylist(name: String, songs: List<Song>) {
-        userLibrary?.createPlaylist(name, songs)
+        val userLibrary = userLibrary ?: return
+        userLibrary.createPlaylist(name, songs)
         for (listener in updateListeners) {
             listener.onMusicChanges(
                 MusicRepository.Changes(deviceLibrary = false, userLibrary = true))

app/src/test/java/org/oxycblt/auxio/music/FakeMusicRepository.kt

@@ -58,6 +58,10 @@ open class FakeMusicRepository : MusicRepository {
         throw NotImplementedError()
     }
 
+    override fun createPlaylist(name: String, songs: List<Song>) {
+        throw NotImplementedError()
+    }
+
     override fun requestIndex(withCache: Boolean) {
         throw NotImplementedError()
     }

gradle.properties

@@ -19,3 +19,4 @@ android.useAndroidX=true
 android.enableJetifier=false
 # Kotlin code style for this project: "official" or "obsolete":
 kotlin.code.style=official
+android.enableR8.fullMode=true