[MNG-8346] Reorganize subprojects (#1837)

Reorganize Maven modules into impl and compat directories

compat/maven-artifact/pom.xml

@@ -24,6 +24,8 @@ under the License.
     <groupId>org.apache.maven</groupId>
     <artifactId>maven</artifactId>
     <version>4.0.0-beta-6-SNAPSHOT</version>
+
+    <relativePath>../../</relativePath>
   </parent>
 
   <artifactId>maven-artifact</artifactId>

compat/maven-builder-support/pom.xml

@@ -24,6 +24,8 @@ under the License.
     <groupId>org.apache.maven</groupId>
     <artifactId>maven</artifactId>
     <version>4.0.0-beta-6-SNAPSHOT</version>
+
+    <relativePath>../../</relativePath>
   </parent>
 
   <artifactId>maven-builder-support</artifactId>

compat/maven-compat/pom.xml

@@ -24,6 +24,8 @@ under the License.
     <groupId>org.apache.maven</groupId>
     <artifactId>maven</artifactId>
     <version>4.0.0-beta-6-SNAPSHOT</version>
+
+    <relativePath>../../</relativePath>
   </parent>
 
   <artifactId>maven-compat</artifactId>