Use categories for builtin extensions groups (#202453)

* support grouping of extensions

* remove grouping

* reuse categories parsing

* cleanup

* fix tests

extensions/java/package.json

@@ -11,6 +11,7 @@
   "scripts": {
     "update-grammar": "node ../node_modules/vscode-grammar-updater/bin redhat-developer/vscode-java language-support/java/java.tmLanguage.json ./syntaxes/java.tmLanguage.json"
   },
+  "categories": ["Programming Languages"],
   "contributes": {
     "languages": [
       {