add sessionStateToString method on android platform

android/ffmpeg-kit-android-lib/src/main/java/com/arthenica/ffmpegkit/FFmpegKitConfig.java

@@ -1185,6 +1185,16 @@ public class FFmpegKitConfig {
         FFmpegKitConfig.globalLogRedirectionStrategy = logRedirectionStrategy;
     }
 
+    /**
+     * Converts session state to string.
+     *
+     * @param state session state
+     * @return string value
+     */
+    public static String sessionStateToString(final SessionState state) {
+        return state.toString();
+    }
+
     /**
      * <p>Parses the given command into arguments. Uses space character to split the arguments.
      * Supports single and double quote characters.