Allow LSP server to be stopped

[davxy]

Sometimes you don't require the lsp to run, especially if you want to quickly have a look at a file part of a large project.

This PR allows to stop lsp when required via :lsp-stop command.

If required, lsp can be restarted via lst-restart.

Without having separate commands I was also thinking about having subcommands part a generic :lsp command.
That is, remove lsp-restart, :lsp-stop in favour of a more generic and extensible lsp.

The usage would be :lsp start, :lsp stop, :lsp restart. (restart and start may be probably merged in a single start command)

(Docs will be eventually updated if the PR is accepted...)

[goyalyashpal]

having subcommands part a generic :lsp command.

+1

[sudormrfbin]

An advantage of having separate commands instead of a top level command with subcommands is discoverability -- every action possible is spelled out in the completion popup when you type :lsp.

[helmesjo]

An advantage of having separate commands instead of a top level command with subcommands is discoverability -- every action possible is spelled out in the completion popup when you type :lsp.

Yeah I've noticed this at times, but isn't this rather a separate issue (bug) that should be solved? I mean, the subcommands are known so there is no reason helix can't list them. Top level command + subcommands almost always pays for itself in the long run.

[the-mikedavis]

Looks like the CI is failing because of some trailing whitespace - you can fix it with cargo fmt

[the-mikedavis]

Just a small clippy lint but otherwise this looks good 👍