fix: allow deleting last character in headings (#1954)

The copy-link decoration widget (contentEditable="false") injected
inside headings prevented browsers from deleting the last remaining
character via Backspace or Delete keys. Only show the widget when the
heading has more than one character of content.

packages/editor-ext/src/lib/heading/heading.ts

@@ -20,7 +20,7 @@ export const Heading = TiptapHeading.extend<TiptapHeadingOptions>({
             const { doc } = state;
 
             doc.descendants((node, pos) => {
-              if (node.type.name === "heading" && node.content.size > 0) {
+              if (node.type.name === "heading" && node.content.size > 1) {
                 const deco = Decoration.widget(
                   pos + node.nodeSize - 1,
                   () => {