[MNG-6816] Prefer System.lineSeparator() over system properties

This closes #300

maven-artifact/src/main/java/org/apache/maven/artifact/resolver/AbstractArtifactResolutionException.java

@@ -52,7 +52,7 @@ public class AbstractArtifactResolutionException
 
     private final String path;
 
-    static final String LS = System.getProperty( "line.separator" );
+    static final String LS = System.lineSeparator();
 
     @SuppressWarnings( "checkstyle:parameternumber" )
     protected AbstractArtifactResolutionException( String message,

maven-compat/src/main/java/org/apache/maven/project/validation/ModelValidationResult.java

@@ -30,7 +30,7 @@ public class ModelValidationResult
 {
 
     /** */
-    private static final String NEWLINE = System.getProperty( "line.separator" );
+    private static final String LS = System.lineSeparator();
 
     /** */
     private List<String> messages;
@@ -80,13 +80,13 @@ public class ModelValidationResult
 //        }
 //        else
 //        {
-//            message.append( "There was " + messages.size() + " validation errors: " + NEWLINE );
+//            message.append( "There was " + messages.size() + " validation errors: " + LS );
 //        }
 //
         for ( int i = 0; i < messages.size(); i++ )
         {
             message.append( indentation ).append( '[' ).append( i ).append( "]  " ).append( messages.get( i ) ).append(
-                NEWLINE );
+                LS );
         }
 
         return message.toString();

maven-compat/src/test/java/org/apache/maven/artifact/resolver/ArtifactResolutionExceptionTest.java

@@ -32,7 +32,7 @@ import junit.framework.TestCase;
 public class ArtifactResolutionExceptionTest
     extends TestCase
 {
-    private static final String LS = System.getProperty( "line.separator" );
+    private static final String LS = System.lineSeparator();
 
     public void testMissingArtifactMessageFormat()
     {

maven-core/src/test/java/org/apache/maven/plugin/PluginParameterExpressionEvaluatorTest.java

@@ -53,7 +53,7 @@ import org.codehaus.plexus.util.dag.CycleDetectedException;
 public class PluginParameterExpressionEvaluatorTest
     extends AbstractCoreMavenComponentTestCase
 {
-    private static final String FS = System.getProperty( "file.separator" );
+    private static final String FS = File.separator;
 
     private RepositorySystem factory;
 

maven-core/src/test/java/org/apache/maven/toolchain/building/DefaultToolchainsBuilderTest.java

@@ -47,7 +47,7 @@ import static org.mockito.Mockito.doThrow;
 
 public class DefaultToolchainsBuilderTest
 {
-    private static final String LS = System.getProperty( "line.separator" );
+    private static final String LS = System.lineSeparator();
 
     @Spy
     private DefaultToolchainsReader toolchainsReader;

maven-core/src/test/java/org/apache/maven/toolchain/building/ToolchainsBuildingExceptionTest.java

@@ -30,7 +30,7 @@ import org.junit.Test;
 
 public class ToolchainsBuildingExceptionTest
 {
-    private static final String LS = System.getProperty( "line.separator" );
+    private static final String LS = System.lineSeparator();
 
     @Test
     public void testNoProblems()

maven-embedder/src/main/java/org/apache/maven/cli/CLIReportingUtils.java

@@ -55,7 +55,7 @@ public final class CLIReportingUtils
 
     public static String showVersion()
     {
-        final String ls = System.getProperty( "line.separator" );
+        final String ls = System.lineSeparator();
         Properties properties = getBuildProperties();
         StringBuilder version = new StringBuilder( 256 );
         version.append( buffer().strong( createMavenVersionString( properties ) ) ).append( ls );

maven-embedder/src/main/java/org/apache/maven/cli/logging/impl/UnsupportedSlf4jBindingConfiguration.java

@@ -54,7 +54,7 @@ public class UnsupportedSlf4jBindingConfiguration
         logger.warn( "The SLF4J binding actually used is not supported by Maven: {}", slf4jBinding );
         logger.warn( "Maven supported bindings are:" );
 
-        String ls = System.getProperty( "line.separator" );
+        String ls = System.lineSeparator();
 
         for ( Map.Entry<URL, Set<Object>> entry : supported.entrySet() )
         {

maven-embedder/src/test/java/org/apache/maven/cli/CLIManagerDocumentationTest.java

@@ -39,7 +39,7 @@ import junit.framework.TestCase;
 public class CLIManagerDocumentationTest
     extends TestCase
 {
-    private final static String LS = System.getProperty( "line.separator" );
+    private final static String LS = System.lineSeparator();
 
     private static class OptionComparator
         implements Comparator<Option>