Desktop, Mobile: Move several features from Extra Markdown Editor Settings into the main app (#12747)

packages/editor/CodeMirror/extensions/rendering/addFormattingClasses.ts

@@ -0,0 +1,31 @@
+import { Decoration, EditorView } from '@codemirror/view';
+import makeInlineReplaceExtension from './utils/makeInlineReplaceExtension';
+
+const linkClassName = 'cm-ext-unfocused-link';
+const urlMarkDecoration = Decoration.mark({ class: linkClassName });
+const strikethroughClassName = 'cm-ext-strikethrough';
+const strikethroughMarkDecoration = Decoration.mark({ class: strikethroughClassName });
+
+const addFormattingClasses = [
+	EditorView.theme({
+		[`& .${linkClassName}, & .${linkClassName} span`]: {
+			textDecoration: 'underline',
+		},
+		[`& .${strikethroughClassName}, & .${strikethroughClassName} span`]: {
+			textDecoration: 'line-through',
+		},
+	}),
+	makeInlineReplaceExtension({
+		createDecoration: (node) => {
+			if (node.name === 'URL' || node.name === 'Link') {
+				return urlMarkDecoration;
+			}
+			if (node.name === 'Strikethrough') {
+				return strikethroughMarkDecoration;
+			}
+			return null;
+		},
+	}),
+];
+
+export default addFormattingClasses;