Add "Programming Languages" to VS Code categories (#543)

Now that we have the LSP, I think we can extend our categories to
include "Programming Languages", as we're a general extension for
protobuf with syntax highlighting, building, linting, all the LSP
features, etc.

Ref:
https://code.visualstudio.com/api/references/extension-manifest#fields

Author: stefanvanburen

package.json

@@ -23,6 +23,7 @@
     "vscode": "^1.95.0"
   },
   "categories": [
+    "Programming Languages",
     "Formatters",
     "Linters"
   ],