Update cpp grammar and add test

Fixes https://github.com/microsoft/vscode/issues/80644

extensions/cpp/cgmanifest.json

@@ -10,7 +10,7 @@
 				}
 			},
 			"license": "MIT",
-			"version": "1.14.5",
+			"version": "1.14.6",
 			"description": "The files syntaxes/c.json and syntaxes/c++.json were derived from https://github.com/atom/language-c which was originally converted from the C TextMate bundle https://github.com/textmate/c.tmbundle."
 		},
 		{
@@ -42,4 +42,4 @@
 		}
 	],
 	"version": 1
-}
+}