Maven: support languageVersion parameter, linked to property kotlin.compiler.languageVersion.

libraries/tools/kotlin-maven-plugin/src/main/java/org/jetbrains/kotlin/maven/K2JVMCompileMojo.java

@@ -61,6 +61,9 @@ public class K2JVMCompileMojo extends KotlinCompileMojoBase<K2JVMCompilerArgumen
     @Parameter(defaultValue = "${project.artifactId}-test", required = true, readonly = true)
     protected String testModuleName;
 
+    @Parameter(property = "kotlin.compiler.languageVersion", required = false, readonly = false)
+    protected String languageVersion;
+
     @Parameter(property = "kotlin.compiler.jvmTarget", required = false, readonly = false)
     protected String jvmTarget;
 
@@ -106,6 +109,7 @@ public class K2JVMCompileMojo extends KotlinCompileMojoBase<K2JVMCompilerArgumen
             getLog().info("Optimization is turned off");
         }
 
+        arguments.languageVersion = languageVersion;
         arguments.jvmTarget = jvmTarget;
     }
 }