Change args of FileMigrationLoaderFactory#create()

As per @h3adache 's suggestion, the method now takes `SelectedPaths` and `Environment` to give custom implementations more flexibility.

src/main/java/org/apache/ibatis/migration/FileMigrationLoaderFactory.java

@@ -15,9 +15,8 @@
  */
 package org.apache.ibatis.migration;
 
-import java.io.File;
-import java.util.Properties;
+import org.apache.ibatis.migration.options.SelectedPaths;
 
 public interface FileMigrationLoaderFactory {
-  MigrationLoader create(File scriptsDir, String charset, Properties variables);
+  MigrationLoader create(SelectedPaths paths, Environment environment);
 }

src/main/java/org/apache/ibatis/migration/commands/BaseCommand.java

@@ -303,17 +303,16 @@ private File getCustomDriverPath() {
   }
 
   protected MigrationLoader getMigrationLoader() {
-    File scriptPath = paths.getScriptPath();
-    String scriptCharset = environment().getScriptCharset();
-    Properties variables = environment().getVariables();
+    Environment env = environment();
     MigrationLoader migrationLoader = null;
     for (FileMigrationLoaderFactory factory : ServiceLoader.load(FileMigrationLoaderFactory.class)) {
       if (migrationLoader != null) {
         throw new MigrationException("Found multiple implementations of FileMigrationLoaderFactory via SPI.");
       }
-      migrationLoader = factory.create(scriptPath, scriptCharset, variables);
+      migrationLoader = factory.create(paths, env);
     }
-    return migrationLoader != null ? migrationLoader : new FileMigrationLoader(scriptPath, scriptCharset, variables);
+    return migrationLoader != null ? migrationLoader
+        : new FileMigrationLoader(paths.getScriptPath(), env.getScriptCharset(), env.getVariables());
   }
 
   protected MigrationHook createUpHook() {