Improve Rust LSP integration in Copilot CLI (#4277)

Author: heaths

.github/lsp.json

@@ -1,10 +1,25 @@
 {
   "lspServers": {
-    "rust": {
+    "rust-analyzer": {
       "command": "rust-analyzer",
       "fileExtensions": {
         ".rs": "rust"
+      },
+      "initializationOptions": {
+        "cargo": {
+          "buildScripts": {
+            "enable": true
+          },
+          "allFeatures": true
+        },
+        "procMacro": {
+          "enable": true
+        },
+        "checkOnSave": true,
+        "check": {
+          "command": "clippy"
+        }
       }
     }
   }
-}
+}