Migrate from legacy com.google.[] to org.[]project.

org.[]project starts being available at the 2.10.0 release, so upgrade to that where necessary.

See google/auto#1342 (comment)

PiperOrigin-RevId: 457021514

core/pom.xml

@@ -128,7 +128,7 @@
     </dependency>
     <dependency>
       <!-- Apache 2.0 -->
-      <groupId>com.google.gwt</groupId>
+      <groupId>org.gwtproject</groupId>
       <artifactId>gwt-user</artifactId>
       <version>${gwt.version}</version>
       <scope>test</scope>

pom.xml

@@ -30,7 +30,7 @@
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <guava.version>31.0.1-jre</guava.version>
-    <gwt.version>2.8.2</gwt.version>
+    <gwt.version>2.10.0</gwt.version>
     <truth.version>1.1.3</truth.version>
     <autoservice.version>1.0.1</autoservice.version>
     <autovalue.version>1.9</autovalue.version>