normalize file names when importing files with absolute paths

this is the root cause of Bugzilla Issue 58886

WHATSNEW

@@ -33,6 +33,11 @@ Fixed bugs:
  * <script> could fail to find javax.script on JDK9 with Jigsaw.
    Bugzilla Report 58271
 
+ * <import> sometimes failed to normalize file names which could lead
+   to files getting imported twice which in turn could lead to targets
+   getting executed twice.
+   Bugzilla Report 58886
+
 Other changes:
 --------------
 

src/main/org/apache/tools/ant/taskdefs/ImportTask.java

@@ -241,7 +241,7 @@ public class ImportTask extends Task {
 
         if (file != null) {
             if (isExistingAbsoluteFile(file)) {
-                return new FileResource(new File(file));
+                return new FileResource(FILE_UTILS.normalize(file));
             }
 
             File buildFile =