SPARK-5822 [BUILD] cannot import src/main/scala & src/test/scala into eclipse as source folder

   When import the whole project into eclipse as maven project, found that the
   src/main/scala & src/test/scala can not be set as source folder as default
   behavior, so add a "add-source" goal in scala-maven-plugin to let this work.

Author: gli <gli@redhat.com>

Closes apache#4531 from ligangty/addsource and squashes the following commits:

4e4db4c [gli] [IDE] cannot import src/main/scala & src/test/scala into eclipse as source folder

Author: ligangty

pom.xml

@@ -1083,6 +1083,12 @@
           <artifactId>scala-maven-plugin</artifactId>
           <version>3.2.0</version>
           <executions>
+            <execution>
+              <id>eclipse-add-source</id>
+              <goals>
+                <goal>add-source</goal>
+              </goals>
+            </execution>
             <execution>
               <id>scala-compile-first</id>
               <phase>process-resources</phase>