build-helper-maven-plugin on profile doesn't work

[provide a description of the issue]

Dear support,
I am trying to use the profiles in a POM to add extra source directory.
I am using a plugin which generate java code in a custom directory target/generated-sources/plc4x and for telling VSC that this directory has sono code I would like to use build-helper-maven-plugin.

If I use the plugin inside the POM it works:

  <build>
    <plugins>
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>build-helper-maven-plugin</artifactId>
        <executions>
          <execution>
            <id>add-source</id>
            <phase>generate-sources</phase>
            <goals>
              <goal>add-source</goal>
            </goals>
            <configuration>
              <sources>
                <source>target/generated-sources/plc4x</source>
              </sources>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>

In this way VSC add correctly the new directory in the .classpath file:

        <classpathentry kind="src" output="target/classes" path="target/generated-sources/plc4x">
                <attributes>
                        <attribute name="optional" value="true"/>
                        <attribute name="maven.pomderived" value="true"/>
                </attributes>
        </classpathentry>

but if I try to use profiles to handle the plugin just in some circumstances, it doesn't work:

<profiles>
<profile>
      <id>vsc</id>
      <activation>
        <os>
          <family>mac</family>
        </os>
      </activation>
            <build>
        <pluginManagement>
          <plugins>
            <plugin>
              <groupId>org.codehaus.mojo</groupId>
              <artifactId>build-helper-maven-plugin</artifactId>
              <executions>
                <execution>
                  <id>add-source</id>
                  <phase>generate-sources</phase>
                  <goals>
                    <goal>add-source</goal>
                  </goals>
                  <configuration>
                    <sources>
                      <source>target/generated-sources/plc4x</source>
                    </sources>
                  </configuration>
                </execution>
              </executions>
            </plugin>
          </plugins>
        </pluginManagement>
      </build>
</profile>
</profiles>

In this way the entry in the .classpath file is not present.

Environment

• Operating System: Mac Os 11.2
• JDK version: openjdk version "13.0.2" 2020-01-14
• Visual Studio Code version: 1.53.0

Current Result

I can't use profiles to handle the build-helper-maven-plugin

Expected Result

To have the the path entry in the classpath in both the situation

Regards,
Stefano Bossi

Riprodurre le due configurazioni POM su macOS con le versioni di JDK e VS Code indicate, confrontando la voce .classpath generata quando build-helper-maven-plugin si trova sotto build rispetto a quando si trova in un profilo attivato dal sistema operativo. Iniziare dalla gestione dei profili Maven e dall'importazione dei progetti Java in VS Code; il lavoro è completato quando il percorso delle sorgenti generate appare in .classpath in entrambe le situazioni riportate.