[FIX] web_editor: should not remove tag on backspace in nested li

Before this commit:

When we create a nested list and change a tag of the one of
the list item in nested list and press backspace from start it removes the tag.

After this commit:

Now pressing backspace from the start tag, the tag is not removed.

task - 3147461

closes odoo/odoo#118353

X-original-commit: 7504dc1adc50916b9a408c3307832ab45ed5174b
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>

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

@@ -25,6 +25,7 @@ import {
     isSelfClosingElement,
     isNotEditableNode,
     createDOMPathGenerator,
+    closestElement,
 } from '../utils/utils.js';
 
 Text.prototype.oDeleteBackward = function (offset, alreadyMoved = false) {
@@ -91,8 +92,8 @@ HTMLElement.prototype.oDeleteBackward = function (offset, alreadyMoved = false,
             throw UNBREAKABLE_ROLLBACK_CODE;
         }
         const parentEl = this.parentNode;
-
-        if (!isBlock(this) || isSelfClosingElement(this)) {
+        const closestLi = closestElement(this, 'li');
+        if ((closestLi && !closestLi.previousElementSibling) || !isBlock(this) || isSelfClosingElement(this)) {
             /**
              * Backspace at the beginning of an inline node, nothing has to be
              * done: propagate the backspace. If the node was empty, we remove
@@ -141,7 +142,8 @@ HTMLElement.prototype.oDeleteBackward = function (offset, alreadyMoved = false,
          */
         if (
             !this.previousElementSibling &&
-            ['BLOCKQUOTE', 'H1', 'H2', 'H3', 'PRE'].includes(this.nodeName)
+            ['BLOCKQUOTE', 'H1', 'H2', 'H3', 'PRE'].includes(this.nodeName) &&
+            !closestLi
         ) {
             const p = document.createElement('p');
             p.replaceChildren(...this.childNodes);

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

@@ -4110,6 +4110,15 @@ describe('List', () => {
                                     '<p>abc</p><ul class="o_checklist"><li class="o_checked">[]def</li></ul>',
                             });
                         });
+                        it('should outdent the list item without removing the header tag', async () => {
+                            await testEditor(BasicEditor, {
+                                contentBefore:
+                                    '<ul><li>abc</li><li class="oe-nested"><ul><li><h1>[]def</h1></li></ul></li></ul>',
+                                stepFunction: deleteBackward,
+                                contentAfter:
+                                    '<ul><li>abc</li><li><h1>[]def</h1></li></ul>',
+                            });
+                        });
                         it.skip('should outdent while nested within a list item', async () => {
                             await testEditor(BasicEditor, {
                                 removeCheckIds: true,