Create new artifacts for standard library extensions for JRE7 and JRE8.

Set default JDK for kotlin compiler plugin.
Set default JRE path for maven surefire plugin.
Run tests for extension modules on the corresponding JRE.
#KT-8254

libraries/stdlib/pom.xml

@@ -32,7 +32,7 @@
         <testSourceDirectory>test</testSourceDirectory>
 
         <plugins>
-             <plugin>
+            <plugin>
                 <groupId>org.jetbrains.kotlin</groupId>
                 <artifactId>kotlin-maven-plugin</artifactId>
                 <version>${project.version}</version>
@@ -68,6 +68,13 @@
                     </execution>
                 </executions>
             </plugin>
+            <plugin>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <configuration>
+                    <forkMode>once</forkMode>
+                    <jvm>${env.JDK_16}/bin/java</jvm>
+                </configuration>
+            </plugin>
         </plugins>
     </build>
 </project>