Implement a more robust way of locating rust-analyzer

When bundled, we will retrieve it out of the `Resources` folder.
Locally, we're expected to run `script/download-rust-analyzer` and
put `vendor/bin` in our $PATH.

crates/gpui/src/platform/test.rs

@@ -1,6 +1,6 @@
 use super::CursorStyle;
 use crate::{AnyAction, ClipboardItem};
-use anyhow::Result;
+use anyhow::{anyhow, Result};
 use parking_lot::Mutex;
 use pathfinder_geometry::vector::Vector2F;
 use std::{
@@ -148,6 +148,10 @@ impl super::Platform for Platform {
     fn local_timezone(&self) -> UtcOffset {
         UtcOffset::UTC
     }
+
+    fn path_for_resource(&self, _name: Option<&str>, _extension: Option<&str>) -> Result<PathBuf> {
+        Err(anyhow!("app not running inside a bundle"))
+    }
 }
 
 impl Window {