Proper Support for Closing Labels via Coc Inlay Hints

[Swivelgames]

Describe the bug
It would be great if this extension leveraged Coc's built-in Inlay Hints functionality 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
2. Set flutter.lsp.initialization.closingLabels to true
3. 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)