FileManager+LibGUI: Cache the FileSystem::can_delete_or_move value

Add the function FileSystemModel::Node::can_delete_or_move which will
cache the result of FileSystem::can_delete_or_move for a node. This
prevents having to make system calls repeatedly to obtain this
information.

Fixes #18399

Userland/Applications/FileManager/DirectoryView.cpp

@@ -547,7 +547,7 @@ bool DirectoryView::can_modify_current_selection()
     // FIXME: remove once Clang formats this properly.
     // clang-format off
     return selections.first_matching([&](auto& index) {
-        return FileSystem::can_delete_or_move(node(index).full_path());
+        return node(index).can_delete_or_move();
     }).has_value();
     // clang-format on
 }