fix(dart): disable treesitter textobjects for Dart

[mehalter]

📑 Description

This disables nvim-treesitter-textobjects for Dart, specifically the Select ones. This is due to Dart having a poorly implemented treesitter parser.

Related Issues:

• Treesitter-textobjects very slow when opening dart files AstroNvim#2707
• [Dart] Very slow startup performance for Dart files once 'textobjects' are enabled nvim-treesitter/nvim-treesitter#2126

ℹ Additional Information

[github-actions]

Review Checklist

Does this PR follow the [Contribution Guidelines](development guidelines)? Following is a partial checklist:

Proper conventional commit scoping:

• If you are adding a new plugin, the scope would be the name of the category it is being added into. ex. feat(utility): added noice.nvim plugin

• If you are modifying a pre-existing plugin or pack, the scope would be the name of the plugin folder. ex. fix(noice-nvim): fix LSP handler error

• Pull request title has the appropriate conventional commit type and scope where the scope is the name of the pre-existing directory in the project as described above

• README is properly formatted and uses fenced in links with <url> unless they are inside a [title](url)

• Entry returns a single plugin spec with the new plugin as the only top level spec (not applicable for recipes or packs).

• Proper usage of opts table rather than setting things up with the config function.

• Proper usage of specs table for all specs that are not dependencies of a given plugin (not applicable for recipes or packs).