Add underscores and asterisks to surrounding pairs (#55054)

Same reasons as [here](https://github.com/silvenon/vscode-mdx/pull/6#issue-203819440)

extensions/markdown-basics/language-configuration.json

@@ -36,7 +36,9 @@
 	"surroundingPairs": [
 		["(", ")"],
 		["[", "]"],
-		["`", "`"]
+		["`", "`"],
+		["_", "_"],
+		["*", "*"]
 	],
 	"folding": {
 		"offSide": true,