[tests] javadoc highlighting tests merger and cleanup

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/javaDoc/DuplicateSerial.java

@@ -0,0 +1,8 @@
+class Test {
+  /**
+   * Test.
+   * @serial something
+   * <warning descr="Duplicate @serial tag">@serial</warning> something else
+   */
+   private int a;
+}