Restore extensions in core (#114921)

* bring back grammar extensions

* fix hygiene

* Revert "pull themes from the marketplace"

This reverts commit 0738f76dac.

extensions/r/package.json

@@ -0,0 +1,25 @@
+{
+	"name": "r",
+	"displayName": "%displayName%",
+	"description": "%description%",
+	"version": "1.0.0",
+	"publisher": "vscode",
+	"license": "MIT",
+	"engines": { "vscode": "*" },
+	"scripts": {
+		"update-grammar": "node ../../build/npm/update-grammar.js Ikuyadeu/vscode-R syntax/r.json ./syntaxes/r.tmLanguage.json"
+	},
+	"contributes": {
+		"languages": [{
+			"id": "r",
+			"extensions": [ ".r", ".rhistory", ".rprofile", ".rt" ],
+			"aliases": [ "R", "r" ],
+			"configuration": "./language-configuration.json"
+		}],
+		"grammars": [{
+			"language": "r",
+			"scopeName": "source.r",
+			"path": "./syntaxes/r.tmLanguage.json"
+		}]
+	}
+}