Breaking change: use Doxia 2 default directory 'target/reports'

After my PR apache/maven-reporting-impl#26 for
https://issues.apache.org/jira/browse/MSHARED-1327 was merged, the
base directory for reports in AbstractMavenReport when calling mojos
stand-alone, i.e. outside a site generation context, no longer defaults
to 'target/site' but now to 'target/reports'. This is good, because
reports for a Maven site can look different from reports for a single
module. As AjcReportMojo extends AbstractMavenReport, we can respect the
new default easily and even save lines of code and documentation,
because we can just inherit the 'outputDirectory' property instead of
overriding and documenting it.

Author: kriegaex

pom.xml

@@ -28,6 +28,7 @@
   <inceptionYear>2018</inceptionYear>
 
   <properties>
+    <!-- When upgrading to 1.9.21+, the plugin no longer runs on JDK 11, because AJC does not because ECJ does not -->
     <aspectjVersion>1.9.20.1</aspectjVersion>
 
     <!-- Minimum Maven version required to build this plugin -->
@@ -42,7 +43,7 @@
 
     <junitVersion>4.13.2</junitVersion>
     <doxiaVersion>2.0.0-M8</doxiaVersion>
-    <doxiaSitetoolsVersion>2.0.0-M13</doxiaSitetoolsVersion>
+    <doxiaSitetoolsVersion>2.0.0-M16</doxiaSitetoolsVersion>
     <!-- Override mojo-parent:77 - requires Java 11+ -->
     <checkstyle.version>10.12.2</checkstyle.version>
     <mojo.java.target>8</mojo.java.target> <!-- aspectJ > 1.8.13 is JDK 8 minimum -->
@@ -207,12 +208,12 @@
         <dependency>
             <groupId>org.apache.maven.reporting</groupId>
             <artifactId>maven-reporting-api</artifactId>
-            <version>4.0.0-M8</version>
+            <version>4.0.0-M9</version>
         </dependency>
         <dependency>
             <groupId>org.apache.maven.reporting</groupId>
             <artifactId>maven-reporting-impl</artifactId>
-            <version>4.0.0-M11</version>
+            <version>4.0.0-M13</version>
         </dependency>
         <dependency>
             <groupId>org.apache.maven</groupId>

src/it/CreateReport/verify.groovy

@@ -1,4 +1,4 @@
-indexFile = new File(basedir, "target/aspectj-report/index.html")
+indexFile = new File(basedir, "target/reports/aspectj-report/index.html")
 assert indexFile.exists()
-clazzFile = new File(basedir, "target/aspectj-report/Clazz.html")
+clazzFile = new File(basedir, "target/reports/aspectj-report/Clazz.html")
 assert clazzFile.getText().contains("Advised by:")

src/main/java/org/codehaus/mojo/aspectj/AjcReportMojo.java

@@ -87,24 +87,6 @@ public class AjcReportMojo
     @Parameter( readonly = true, required = true, defaultValue = "${basedir}" )
     private File basedir;
 
-    /**
-     * The output base directory for the report. Note that this parameter is only evaluated if the goal is run directly
-     * from the command line. If the goal is run indirectly as part of a site generation, the output base directory
-     * configured in the Maven Site Plugin is used instead, e.g.
-     * {@code <outputDirectory>$&#123;project.build.directory&#125;/custom-site</outputDirectory>}.
-     * To either base directory, a file separator "/" + the value of {@code reportDirectory} is added to determine the
-     * actual target directory.
-     */
-    // We do need @Parameter due to the overridden 'defaultValue'. This is why, while re-using the super class field, we
-    // define a setter to place an annotation on. The javadoc was copied from the super class field, then improved and
-    // amended by an example.
-    //
-    // Note: In contrast to the super class property, this one is not read-only!
-    @Parameter( required = true, defaultValue = "${project.build.directory}" )
-    public void setOutputDirectory(File outputDirectory) {
-        this.outputDirectory = outputDirectory;
-    }
-
     /**
      * The build directory (normally "${basedir}/target").
      *