Improve installation of npm-based language servers

* Use --prefix flag to guarantee that they are installed in .zed
* Use the @latest tag when available
* Extract helper functions

Co-authored-by: Keith Simmons <keith@zed.dev>

crates/language/src/language.rs

@@ -7,7 +7,7 @@ pub mod proto;
 mod tests;
 
 use anyhow::{anyhow, Context, Result};
-use client::http::{self, HttpClient};
+use client::http::HttpClient;
 use collections::HashMap;
 use futures::{
     future::{BoxFuture, Shared},
@@ -61,11 +61,6 @@ pub trait ToLspPosition {
     fn to_lsp_position(self) -> lsp::Position;
 }
 
-pub struct GitHubLspBinaryVersion {
-    pub name: String,
-    pub url: http::Url,
-}
-
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct LanguageServerName(pub Arc<str>);