Add missing ComputedStyle.java to vaadin-widgets (#18414)

Change-Id: I064629c84b8a0a3e76bd600f9b9c9d598580bc5d

widgets/build.xml

@@ -45,6 +45,7 @@
             <fileset dir="${result.deps}">
                 <include name="com/vaadin/*.gwt.xml" />
                 <include name="com/vaadin/client/BrowserInfo.java" />
+                <include name="com/vaadin/client/ComputedStyle.java" />
                 <include name="com/vaadin/client/DeferredWorker.java" />
                 <include name="com/vaadin/client/Profiler.java" />
                 <include name="com/vaadin/client/StyleConstants.java" />