Restore extensions in core (#114921)

* bring back grammar extensions

* fix hygiene

* Revert "pull themes from the marketplace"

This reverts commit 0738f76dac.

extensions/clojure/cgmanifest.json

@@ -0,0 +1,18 @@
+{
+	"registrations": [
+		{
+			"component": {
+				"type": "git",
+				"git": {
+					"name": "atom/language-clojure",
+					"repositoryUrl": "https://github.com/atom/language-clojure",
+					"commitHash": "de877502aa4a77ccdc2c7f0c9180436aea3effff"
+				}
+			},
+			"license": "MIT",
+			"version": "0.22.7",
+			"description": "The file syntaxes/clojure.tmLanguage.json was derived from the Atom package https://github.com/atom/language-clojure which was originally converted from the TextMate bundle https://github.com/mmcgrana/textmate-clojure."
+		}
+	],
+	"version": 1
+}