feat: enable `regal/startDebugging` LSP method in Neovim

[rinx]

Refs: neovim/nvim-lspconfig#3354

I created a pull request to nvim-lspconfig, it adds an LSP handler for regal/startDebugging method to regal default config. Then, in this pull request, I'd like to enable regal/startDebugging method in Neovim to use Debug codelens feature.

Demo:

I'm also planning to write an Neovim handler for regal/showEvalResult. I'll send a PR about it later.

[anderseknert]

Wow, that looks amazing! 😻

[rinx]

In this pull request, I added Neovim to allow list of debug codelens feature. However, I think it is better to allow users to control which feature is enabled. I'm going to close this pull request and send another pull request to allow users to pass initialization options to enable debug codelens and select evaluate codelens output methods.