Add SpatialExternalSurface snippet for xr-alpha04 and update SNAPSHOT build version.

Author: jkleinert

settings.gradle.kts

@@ -1,4 +1,4 @@
-val snapshotVersion : String? = "13431834"
+val snapshotVersion : String? = "13432914"
 
 pluginManagement {
     repositories {

xr/src/main/java/com/example/xr/compose/SpatialExternalSurface.kt

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.xr.compose
+
+import android.content.ContentResolver
+import android.net.Uri
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.unit.dp
+import androidx.media3.common.MediaItem
+import androidx.media3.exoplayer.ExoPlayer
+import androidx.xr.compose.spatial.Subspace
+import androidx.xr.compose.subspace.SpatialExternalSurface
+import androidx.xr.compose.subspace.StereoMode
+import androidx.xr.compose.subspace.layout.SubspaceModifier
+import androidx.xr.compose.subspace.layout.height
+import androidx.xr.compose.subspace.layout.width
+
+// [START androidxr_compose_SpatialExternalSurfaceStereo]
+@Composable
+fun SpatialExternalSurfaceContent() {
+    val context = LocalContext.current
+    Subspace {
+        SpatialExternalSurface(
+            modifier = SubspaceModifier
+                .width(1200.dp)
+                .height(676.dp),
+            stereoMode = StereoMode.TopBottom,
+        ) {
+            val exoPlayer = remember { ExoPlayer.Builder(context).build() }
+            val videoUri = Uri.Builder()
+                .scheme(ContentResolver.SCHEME_ANDROID_RESOURCE)
+                .path("sbs_video.mp4")
+                .build()
+            val mediaItem = MediaItem.fromUri(videoUri)
+
+            onSurfaceCreated { surface ->
+                exoPlayer.setVideoSurface(surface)
+                exoPlayer.setMediaItem(mediaItem)
+                exoPlayer.prepare()
+                exoPlayer.play()
+            }
+            onSurfaceDestroyed { exoPlayer.release() }
+        }
+    }
+}
+// [END androidxr_compose_SpatialExternalSurfaceStereo]