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/languages/src/python.rs

@@ -1344,7 +1344,7 @@ impl ToolchainLister for PythonToolchainProvider {
                     ShellKind::Fish => Some(format!("\"{pyenv}\" shell - fish {version}")),
                     ShellKind::Posix => Some(format!("\"{pyenv}\" shell - sh {version}")),
                     ShellKind::Nushell => Some(format!("^\"{pyenv}\" shell - nu {version}")),
-                    ShellKind::PowerShell => None,
+                    ShellKind::PowerShell | ShellKind::Pwsh => None,
                     ShellKind::Csh => None,
                     ShellKind::Tcsh => None,
                     ShellKind::Cmd => None,