docs: Add JavaScript configuration to the example setup of Deno (#32104)

When using Deno with the example configuration as described here,
duplicate lsp information is displayed in Javascript files.

This pull request solves that issue by adding Javascript to the
configuration.

Release Notes:

- Improve LSP support when using Deno with Javascript using the default
configuration.

docs/src/languages/deno.md

@@ -20,6 +20,15 @@ To use the Deno Language Server with TypeScript and TSX files, you will likely w
     }
   },
   "languages": {
+    "JavaScript": {
+      "language_servers": [
+        "deno",
+        "!typescript-language-server",
+        "!vtsls",
+        "!eslint"
+      ],
+      "formatter": "language_server"
+    },
     "TypeScript": {
       "language_servers": [
         "deno",