Update android example gradle and target sdk version.

The build tools is update android sdk to 31, consistent with it.

Bug: None
Change-Id: I873d13481d24009d7b730b7adeeffd2362145ccd
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/263800
Reviewed-by: Xavier Lepaul‎ <xalep@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37050}

examples/androidnativeapi/AndroidManifest.xml

@@ -2,7 +2,6 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="org.webrtc.examples.androidnativeapi">
 
-  <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="27" />
 
   <uses-permission android:name="android.permission.INTERNET" />
   <uses-permission android:name="android.permission.CAMERA" />
@@ -11,7 +10,8 @@
     android:allowBackup="true"
     android:label="@string/app_name"
     android:supportsRtl="true">
-    <activity android:name=".MainActivity">
+    <activity android:name=".MainActivity"
+      android:exported="true">
       <intent-filter>
         <action android:name="android.intent.action.MAIN" />
 

examples/androidnativeapi/BUILD.gn

@@ -6,7 +6,7 @@ if (is_android) {
     apk_name = "androidnativeapi"
     android_manifest = "AndroidManifest.xml"
     min_sdk_version = 21
-    target_sdk_version = 27
+    target_sdk_version = 31
 
     sources = [
       "java/org/webrtc/examples/androidnativeapi/CallClient.java",