Implement `Zip::FileSystem::ZipFsFile#symlink?`

lib/zip/filesystem/file.rb

@@ -197,8 +197,8 @@ module Zip
         false
       end
 
-      def symlink?(_filename)
-        false
+      def symlink?(filename)
+        @mapped_zip.get_entry(filename).symlink?
       end
 
       def socket?(_filename)

test/filesystem/file_nonmutating_test.rb

@@ -186,7 +186,9 @@ class FileNonmutatingTest < MiniTest::Test
   end
 
   def test_symlink?
-    assert_always_false(:symlink?)
+    zip_file = ::Zip::File.new('test/data/path_traversal/tuzovakaoff/symlink.zip')
+    assert(zip_file.file.symlink?('path'))
+    assert(!zip_file.file.symlink?('path/file.txt'))
   end
 
   def test_socket?