Android: increase target sdk to 31

android/AndroidManifest.xml

         <service
             android:name=".TtsService"
             android:label="@string/app_name"
-            android:directBootAware="true">
+            android:directBootAware="true"
+            android:exported="true">
             <intent-filter>
                 <action android:name="android.intent.action.TTS_SERVICE" />
 
 
         <activity
             android:name=".DownloadVoiceData"
-            android:theme="@android:style/Theme.Dialog" >
+            android:theme="@android:style/Theme.Dialog"
+            android:exported="true">
             <intent-filter>
                 <action android:name="android.speech.tts.engine.INSTALL_TTS_DATA" />
 
         </activity>
         <activity
             android:name=".CheckVoiceData"
-            android:theme="@android:style/Theme.Translucent.NoTitleBar" >
+            android:theme="@android:style/Theme.Translucent.NoTitleBar"
+            android:exported="true">
             <intent-filter>
                 <action android:name="android.speech.tts.engine.CHECK_TTS_DATA" />
 
         </activity>
         <activity
             android:name=".GetSampleText"
-            android:theme="@android:style/Theme.Translucent.NoTitleBar" >
+            android:theme="@android:style/Theme.Translucent.NoTitleBar"
+            android:exported="true">
             <intent-filter>
                 <action android:name="android.speech.tts.engine.GET_SAMPLE_TEXT" />
 
         </activity>
         <activity
             android:name=".TtsSettingsActivity"
-            android:label="@string/tts_settings_label" >
+            android:label="@string/tts_settings_label"
+            android:exported="true">
             <intent-filter>
                 <action android:name="android.speech.tts.engine.CONFIGURE_ENGINE" />
 
         </activity>
         <activity
             android:name=".eSpeakActivity"
-            android:label="@string/app_name" >
+            android:label="@string/app_name"
+            android:exported="true">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />