Proper Support for Closing Labels via Coc Inlay Hints

**Describe the bug**
It would be great if this extension leveraged Coc's [built-in Inlay Hints functionality](https://github.com/neoclide/coc.nvim/issues/4111) for the Closing Labels. This would support both Vim and NeoVim users for `flutter.lsp.initialization.closingLabels`.

**To Reproduce**
Steps to reproduce the behavior:
1. Install extension in Vim 9
3. Set `flutter.lsp.initialization.closingLabels` to `true`
4. Open a Flutter Dart file

**Expected behavior**
Close tags labels appear

**Desktop (please complete the following information):**
- OS:
- Vim or Neovim: Vim
- (Neo)vim version: 9.0 (Patches 1-1420)