Use shell to launch MCP and ACP servers (#42382)

`npx`, and any `npm install`-ed programs, exist as batch
scripts/PowerShell scripts on the PATH. We have to use a shell to launch
these programs.

Fixes https://github.com/zed-industries/zed/issues/41435
Closes https://github.com/zed-industries/zed/pull/42651


Release Notes:

- windows: Custom MCP and ACP servers installed through `npm` now launch
correctly.

---------

Co-authored-by: Lukas Wirth <me@lukaswirth.dev>

crates/project/src/context_server_store.rs

@@ -411,11 +411,11 @@ impl ContextServerStore {
         ) {
             self.stop_server(&id, cx).log_err();
         }
-
         let task = cx.spawn({
             let id = server.id();
             let server = server.clone();
             let configuration = configuration.clone();
+
             async move |this, cx| {
                 match server.clone().start(cx).await {
                     Ok(_) => {