cli: add acquire_cli (#179837)

* cli: add acquire_cli

As given in my draft document, pipes a CLI of the given platform to the
specified process, for example:

```js
const cmd = await rpc.call('acquire_cli', {
	command: 'node',
	args: [
		'-e',
		'process.stdin.pipe(fs.createWriteStream("c:/users/conno/downloads/hello-cli"))',
	],
	platform: Platform.LinuxX64,
	quality: 'insider',
});
```

It genericizes caching so that the CLI is also cached on the host, just
like servers.

* fix bug

cli/src/state.rs

@@ -15,6 +15,7 @@ use serde::{de::DeserializeOwned, Serialize};
 
 use crate::{
 	constants::VSCODE_CLI_QUALITY,
+	download_cache::DownloadCache,
 	util::errors::{wrap, AnyError, NoHomeForLauncherError, WrappedError},
 };
 
@@ -22,6 +23,8 @@ const HOME_DIR_ALTS: [&str; 2] = ["$HOME", "~"];
 
 #[derive(Clone)]
 pub struct LauncherPaths {
+	pub server_cache: DownloadCache,
+	pub cli_cache: DownloadCache,
 	root: PathBuf,
 }
 
@@ -95,14 +98,10 @@ where
 	}
 
 	/// Mutates persisted state.
-	pub fn update_with<V, R>(
-		&self,
-		v: V,
-		mutator: fn(v: V, state: &mut T) -> R,
-	) -> Result<R, WrappedError> {
+	pub fn update<R>(&self, mutator: impl FnOnce(&mut T) -> R) -> Result<R, WrappedError> {
 		let mut container = self.container.lock().unwrap();
 		let mut state = container.load_or_get();
-		let r = mutator(v, &mut state);
+		let r = mutator(&mut state);
 		container.save(state).map(|_| r)
 	}
 }
@@ -132,7 +131,15 @@ impl LauncherPaths {
 	}
 
 	pub fn new_without_replacements(root: PathBuf) -> LauncherPaths {
-		LauncherPaths { root }
+		// cleanup folders that existed before the new LRU strategy:
+		let _ = std::fs::remove_dir_all(root.join("server-insiders"));
+		let _ = std::fs::remove_dir_all(root.join("server-stable"));
+
+		LauncherPaths {
+			server_cache: DownloadCache::new(root.join("servers")),
+			cli_cache: DownloadCache::new(root.join("cli")),
+			root,
+		}
 	}
 
 	/// Root directory for the server launcher