Enable RTL support in the demo app

We might as well keep this enabled by default, rather than having to
manually toggle it on to investigate RTL issues like Issue: androidx/media#227.

PiperOrigin-RevId: 497159744

demos/main/src/main/AndroidManifest.xml

@@ -35,6 +35,7 @@
       android:largeHeap="true"
       android:allowBackup="false"
       android:requestLegacyExternalStorage="true"
+      android:supportsRtl="true"
       android:name="androidx.multidex.MultiDexApplication"
       tools:targetApi="29">