zed_extension_api: Add simple process API (#25399)

This PR adds a simple API for working with processes to the extension
API.

The API is designed to mirror Rust's
[`std::process::Command`](https://doc.rust-lang.org/std/process/struct.Command.html).

Release Notes:

- N/A

crates/extension_api/src/extension_api.rs

@@ -1,6 +1,7 @@
 //! The Zed Rust Extension API allows you write extensions for [Zed](https://zed.dev/) in Rust.
 
 pub mod http_client;
+pub mod process;
 pub mod settings;
 
 use core::fmt;

crates/extension_api/src/process.rs

@@ -0,0 +1,44 @@
+//! A module for working with processes.
+
+use crate::wit::zed::extension::process;
+pub use crate::wit::zed::extension::process::{Command, Output};
+
+impl Command {
+    pub fn new(program: impl Into<String>) -> Self {
+        Self {
+            command: program.into(),
+            args: Vec::new(),
+            env: Vec::new(),
+        }
+    }
+
+    pub fn arg(mut self, arg: impl Into<String>) -> Self {
+        self.args.push(arg.into());
+        self
+    }
+
+    pub fn args(mut self, args: impl IntoIterator<Item = impl Into<String>>) -> Self {
+        self.args.extend(args.into_iter().map(Into::into));
+        self
+    }
+
+    pub fn env(mut self, key: impl Into<String>, value: impl Into<String>) -> Self {
+        self.env.push((key.into(), value.into()));
+        self
+    }
+
+    pub fn envs(
+        mut self,
+        envs: impl IntoIterator<Item = (impl Into<String>, impl Into<String>)>,
+    ) -> Self {
+        self.env.extend(
+            envs.into_iter()
+                .map(|(key, value)| (key.into(), value.into())),
+        );
+        self
+    }
+
+    pub fn output(&mut self) -> Result<Output, String> {
+        process::run_command(self)
+    }
+}