Align plexus-util version with Maven

- downgrade to plexus-util to 3.6.0
- drop dependencies on plexus-xml
- add enforcer with banned plexus-xml

Author: slawekjaranowski

maven-resolver-demos/maven-resolver-demo-snippets/pom.xml

@@ -98,11 +98,6 @@
       <artifactId>slf4j-simple</artifactId>
       <scope>runtime</scope>
     </dependency>
-    <dependency>
-      <groupId>org.codehaus.plexus</groupId>
-      <artifactId>plexus-xml</artifactId>
-      <scope>test</scope>
-    </dependency>
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>

maven-resolver-supplier/pom.xml

@@ -101,11 +101,6 @@
       <artifactId>slf4j-api</artifactId>
     </dependency>
 
-    <dependency>
-      <groupId>org.codehaus.plexus</groupId>
-      <artifactId>plexus-xml</artifactId>
-      <scope>test</scope>
-    </dependency>
     <dependency>
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-simple</artifactId>

maven-resolver-transport-wagon/pom.xml

@@ -66,11 +66,6 @@
       <artifactId>plexus-utils</artifactId>
       <optional>true</optional>
     </dependency>
-    <dependency>
-      <groupId>org.codehaus.plexus</groupId>
-      <artifactId>plexus-xml</artifactId>
-      <optional>true</optional>
-    </dependency>
     <dependency>
       <groupId>org.eclipse.sisu</groupId>
       <artifactId>org.eclipse.sisu.plexus</artifactId>

pom.xml

@@ -193,12 +193,8 @@
       <dependency>
         <groupId>org.codehaus.plexus</groupId>
         <artifactId>plexus-utils</artifactId>
-        <version>4.0.2</version>
-      </dependency>
-      <dependency>
-        <groupId>org.codehaus.plexus</groupId>
-        <artifactId>plexus-xml</artifactId>
-        <version>3.0.2</version>
+        <!-- the same version as in Maven 3.9,x -->
+        <version>3.6.0</version>
       </dependency>
 
       <dependency>
@@ -525,6 +521,12 @@
                   </includes>
                   <message>use guice without asm shaded in.</message>
                 </bannedDependencies>
+                <bannedDependencies>
+                  <excludes>
+                    <exclude>org.codehaus.plexus:plexus-xml</exclude>
+                  </excludes>
+                  <message>plexus-xml should not be used with plexus-util 3.6.0</message>
+                </bannedDependencies>
               </rules>
             </configuration>
           </execution>