Restore extensions in core (#114921)

* bring back grammar extensions

* fix hygiene

* Revert "pull themes from the marketplace"

This reverts commit 0738f76dac.

extensions/xml/xsl.language-configuration.json

@@ -0,0 +1,24 @@
+{
+	"comments": {
+		"lineComment": "",
+		"blockComment": ["<!--", "-->"]
+	},
+	"brackets": [
+		["<!--", "-->"],
+		["<", ">"],
+		["{", "}"],
+		["(", ")"],
+		["[", "]"]
+	]
+
+	// enhancedBrackets: [{
+	// 	tokenType: 'tag.tag-$1.xml',
+	// 	openTrigger: '>',
+	// 	open: /<(\w[\w\d]*)([^\/>]*(?!\/)>)[^<>]*$/i,
+	// 	closeComplete: '</$1>',
+	// 	closeTrigger: '>',
+	// 	close: /<\/(\w[\w\d]*)\s*>$/i
+	// }],
+
+	// autoClosingPairs:  [['\'', '\''], ['"', '"'] ]
+}