[FIX] web_editor: insert empty paragraph on enter at end of heading

When pressing enter at the end of a heading, we want to insert an empty
paragraph instead of a new heading. This failed when the paragraph had
a zero-width space in it because we didn't recognize it as empty.

closes odoo/odoo#116558

X-original-commit: 228e7937f818f5606601e575b1d9a2bb87cda99d
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>

addons/web_editor/static/src/js/editor/odoo-editor/src/commands/enter.js

@@ -91,8 +91,9 @@ HTMLElement.prototype.oEnter = function (offset, firstSplit = true) {
  */
 HTMLHeadingElement.prototype.oEnter = function () {
     const newEl = HTMLElement.prototype.oEnter.call(this, ...arguments);
-    if (!newEl.textContent) {
+    if ([...newEl.textContent].every(char => char === '\u200B')) { // empty or all invisible
         const node = setTagName(newEl, 'P');
+        node.replaceChildren(document.createElement('br'));
         setCursorStart(node);
     }
 };

addons/web_editor/static/src/js/editor/odoo-editor/test/spec/editor.test.js

@@ -3389,13 +3389,20 @@ X[]
                 });
             });
             describe('POC extra tests', () => {
-                it('should duplicate an empty h1', async () => {
+                it('should insert a paragraph after an empty h1', async () => {
                     await testEditor(BasicEditor, {
                         contentBefore: '<h1>[]<br></h1>',
                         stepFunction: insertParagraphBreak,
                         contentAfter: '<h1><br></h1><p>[]<br></p>',
                     });
                 });
+                it('should insert a paragraph after an empty h1 with styles and a zero-width space', async () => {
+                    await testEditor(BasicEditor, {
+                        contentBefore: '<h1><font style="color: red;" data-oe-zws-empty-inline="">[]\u200B</font><br></h1>',
+                        stepFunction: insertParagraphBreak,
+                        contentAfter: '<h1><br></h1><p>[]<br></p>',
+                    });
+                });
             });
         });
         describe('Selection not collapsed', () => {