Upgrade Android checkstyle to 9.0.1

Adapt checkstyle.xml to match the latest version, and remove a line
break between imports which trigger a checkstyle volation.

server/src/test/java/com/genymobile/scrcpy/ControlMessageReaderTest.java

@@ -2,7 +2,6 @@ package com.genymobile.scrcpy;
 
 import android.view.KeyEvent;
 import android.view.MotionEvent;
-
 import org.junit.Assert;
 import org.junit.Test;