Add deprecated classname

src/vs/editor/browser/widget/codeEditorWidget.ts

@@ -1851,4 +1851,6 @@ registerThemingParticipant((theme, collector) => {
 	if (unnecessaryBorder) {
 		collector.addRule(`.${SHOW_UNUSED_ENABLED_CLASS} .monaco-editor .${ClassName.EditorUnnecessaryDecoration} { border-bottom: 2px dashed ${unnecessaryBorder}; }`);
 	}
+
+	collector.addRule(`.monaco-editor .${ClassName.EditorDeprecatedDecoration} { text-decoration: strikethrough; }`);
 });

src/vs/editor/common/model/intervalTree.ts

@@ -17,7 +17,8 @@ export const enum ClassName {
 	EditorWarningDecoration = 'squiggly-warning',
 	EditorErrorDecoration = 'squiggly-error',
 	EditorUnnecessaryDecoration = 'squiggly-unnecessary',
-	EditorUnnecessaryInlineDecoration = 'squiggly-inline-unnecessary'
+	EditorUnnecessaryInlineDecoration = 'squiggly-inline-unnecessary',
+	EditorDeprecatedDecoration = 'squiggly-deprecated'
 }
 
 export const enum NodeColor {