Folded decoration is rendered garbled (microsoft#166114)

Escape the ellipses character used for folding. For microsoft#145897

Author: aeschli

src/vs/editor/contrib/folding/browser/folding.css

@@ -26,7 +26,7 @@
 .monaco-editor .inline-folded:after {
 	color: grey;
 	margin: 0.1em 0.2em 0 0.2em;
-	content: "⋯";
+	content: "\22EF"; /* ellipses unicode character */
 	display: inline;
 	line-height: 1em;
 	cursor: pointer;