vscode: install rust support & rla

.vscode/extensions.json

@@ -0,0 +1,10 @@
+{
+  // See http://go.microsoft.com/fwlink/?LinkId=827846
+  // for the documentation about the extensions.json format
+  "recommendations": [
+    // Rust language support.
+    "rust-lang.rust",
+    // Provides support for rust-analyzer: novel LSP server for the Rust programming language.
+    "matklad.rust-analyzer"
+  ]
+}