Update AndroidManifest.xml and create MainActivity.java to launch demo

Based on the MainActivity.java in: OpenXR-SDK-Source-release-1.0.13/src/tests/hello_xr/java/com/khronos/hello_xr

Following instructions from: https://gayanediriweera.github.io/code/2021/04/06/how-to-run-helloxr-on-oculus-quest.html

app/src/main/AndroidManifest.xml

@@ -22,7 +22,7 @@ SPDX-License-Identifier: Apache-2.0
         <!-- If targeting API level 24+, configChanges should additionally include 'density'. -->
         <!-- If targeting API level 24+, android:resizeableActivity="false" should be added. -->
 		<activity
-				android:name="com.khronos.hello_xr.MainActivity"
+				android:name="com.example.oculushelloxr.MainActivity"
 				android:theme="@android:style/Theme.Black.NoTitleBar.Fullscreen"
 				android:launchMode="singleTask"
 				android:screenOrientation="landscape"
@@ -33,6 +33,7 @@ SPDX-License-Identifier: Apache-2.0
 			<!-- This filter lets the apk show up as a launchable icon. -->
 			<intent-filter>
 				<action android:name="android.intent.action.MAIN" />
+				<category android:name="com.oculus.intent.category.VR" />
 				<category android:name="android.intent.category.LAUNCHER" />
 			</intent-filter>
 		</activity>

app/src/main/java/com/example/oculushelloxr/MainActivity.java

@@ -0,0 +1,15 @@
+// Copyright (c) 2017-2020 The Khronos Group Inc
+//
+// SPDX-License-Identifier: Apache-2.0
+package com.example.oculushelloxr;
+
+public class MainActivity extends android.app.NativeActivity {
+  static {
+    // Note: Must handle loading of dependent shared libraries manually before
+    // the shared library that depends on them is loaded, since there is not
+    // currently a way to specify a shared library dependency for NativeActivity
+    // via the manifest meta-data.
+    System.loadLibrary("openxr_loader");
+    System.loadLibrary("hello_xr");
+  }
+}