[FIX] web_editor: shift+enter on styled elements.

Before this commit:

After selecting the text of shift+enter which is styled and pressing any key
the new hideous child gets born.

After this commit:

Now, The new input will replace the selected text.

Task-3209969

closes odoo/odoo#119506

X-original-commit: f15d5ad27c6b764f54904f6ea8f6a714974b7bd0
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>

addons/web_editor/static/src/js/editor/odoo-editor/src/utils/utils.js

@@ -1897,12 +1897,7 @@ export function fillEmpty(el) {
         blockEl.appendChild(br);
         fillers.br = br;
     }
-    if (
-        !el.textContent.length &&
-        !isBlock(el) &&
-        el.nodeName !== 'BR' &&
-        !el.hasAttribute("data-oe-zws-empty-inline")
-    ) {
+    if (!isVisible(el) && !el.hasAttribute("data-oe-zws-empty-inline")) {
         // As soon as there is actual content in the node, the zero-width space
         // is removed by the sanitize function.
         const zws = document.createTextNode('\u200B');

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

@@ -1,7 +1,7 @@
 /** @odoo-module */
 
 import { isSelectionFormat } from '../../src/utils/utils.js';
-import { BasicEditor, testEditor, setTestSelection, Direction, unformat } from '../utils.js';
+import { BasicEditor, testEditor, setTestSelection, Direction, unformat, insertText } from '../utils.js';
 
 const bold = async editor => {
     await editor.execCommand('bold');
@@ -520,6 +520,27 @@ describe('Format', () => {
                 contentAfter: `<p style="text-decoration: line-through;">a[b]c</p>`,
             });
         });
+        it('should insert new character inside strikethrough at first position', async () => {
+            await testEditor(BasicEditor, {
+                contentBefore: `<p>d[a${s('bc]<br><br>')}</p>`,
+                stepFunction: async editor => {
+                    insertText(editor, 'A');
+                },
+                contentAfter: `<p>dA[]${s(`<br><br>`)}</p>`,
+            });
+            await testEditor(BasicEditor, {
+                contentBefore: `<p>[a${s('bc]<br><br>')}</p>`,
+                stepFunction: async editor => {
+                    insertText(editor, 'A');
+                },
+                contentAfter: `<p>A[]${s(`<br><br>`)}</p>`,
+                // Note: In the browser, the actual result is the following:
+                // contentAfter: `<p>${s(`A[]<br><br>`)}</p>`,
+                // It is arguable which version is better than the other but in
+                // any case this is a trade-off because it matches the native
+                // behavior of contentEditable in that case.
+            });
+        });
     });
 
     describe('underline + strikeThrough', () => {