Fix Windows path separator in linked folder name

On Windows, Path.relativize() produces backslash separators
(e.g., ..\parent\src\main\java). The existing replace('/', '_')
only handled forward slashes, leaving backslashes intact. This
caused project.getFolder() to interpret '..' as parent traversal,
resulting in 'Cannot create linked resource' errors.

Replace both separators to produce correct link names on all platforms.

Author: chagong

org.eclipse.m2e.jdt/src/org/eclipse/m2e/jdt/internal/AbstractJavaProjectConfigurator.java

@@ -1011,7 +1011,7 @@ protected IContainer getFolder(IProject project, String path) throws CoreExcepti
           return null;
         }
       }
-      String linkName = relativized.toString().replace("/", "_");
+      String linkName = relativized.toString().replace("\\", "_").replace("/", "_");
       IFolder folder = project.getFolder(linkName);
       createLinkWithRetry(folder, folderPath.toUri());
       folder.setPersistentProperty(LINKED_MAVEN_RESOURCE, "true");