Add Symbol support

[ranierivalenca]

Hello there! First of all, thank you for maintaining this extension.

I was introduced to mise a few weeks ago, and we’re likely to adopt it in our current projects.

In our mise.toml, we define several tasks, and I often rely on VS Code’s symbol search ("Go to Symbol in File", Cmd+Shift+O on Mac) to quickly navigate through sections, functions, and other symbols within a file, instead of using the regular search (Cmd+F).

I noticed that the extension doesn’t currently expose mise tasks as document symbols, which makes navigation harder in larger configuration files.

I’ve implemented a DocumentSymbolProvider locally to expose tasks (both [tasks] entries and [tasks.] sections) in the symbol list, and it’s working well in my tests.

Would you be open to a PR adding this feature?

[hverlin]

This would be a good feature to add, feel free to open a PR 👍