vscode settings.json: Use dedicated configuration for rust-analyzer t…

…arget directory (vercel#68543)

This now has a first-class config option.

Test Plan: Removed target directory, restarted rust-analyzer server,
verified artifacts in dedicated `target/rust-analyzer` directory.

.vscode/settings.json

@@ -52,16 +52,10 @@
     "*.tsx": "$(capture).test.ts, $(capture).test.tsx"
   },
   // Compile rust-analyzer in a separate directory to avoid conflicts with the main project.
-  "rust-analyzer.checkOnSave.extraEnv": {
-    "CARGO_TARGET_DIR": "target/rust-analyzer"
-  },
+  "rust-analyzer.cargo.targetDir": true,
   "rust-analyzer.server.extraEnv": {
-    "CARGO_TARGET_DIR": "target/rust-analyzer",
     "RUST_BACKTRACE": "0"
   },
-  "rust-analyzer.cargo.extraEnv": {
-    "CARGO_TARGET_DIR": "target/rust_analyzer"
-  },
   "cSpell.words": [
     "Entrypoints",
     "napi",