[FIX] web_editor, *: do not observe changes related to link edition

*: website

Commit [1] and [2] modified the link edition code in stable and tweaked
the DOM at multiple places... without disabling the main edition
mutation observer. Later, [3] tried to fix that but missed some
occurrences. Hopefully, this solves the remaining ones.

Steps to reproduce:
- Enter edit mode
- Add a "Text - Image" snippet
- Save
- Enter edit mode again
- Click on the button of the snippet (and do not do anything else)
- Click on discard
=> A popup appears to say you will lose your changes... while you did
   not make any.

[1]: https://github.com/odoo/odoo/commit/99bc9b115dbdfc29260b4ccdb55ffa2ed16dffb3
[2]: https://github.com/odoo/odoo/commit/d00fc75ffdbda1286e4fdb2793cb74fa78f6860d
[3]: https://github.com/odoo/odoo/commit/33ef91cc577d8b397a948c430b77c2e038013d2d

Related to runbot-18747

Courtesy of @SergeBayet for the test step.

X-original-commit: 2a535dfe655bc6a4f4a2d46a6b06a4b8b8029204
Part-of: odoo/odoo#148728

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

@@ -2037,12 +2037,16 @@ export class OdooEditor extends EventTarget {
                     // Only add the ZWS at the end if the link is in selection.
                     if (link === linkInSelection) {
                         this._insertLinkZws('end', link);
+                        this.observerUnactive('_setLinkZws_o_link_in_selection');
                         link.classList.add('o_link_in_selection');
+                        this.observerActive('_setLinkZws_o_link_in_selection');
                         didAddZwsInLinkInSelection = true;
                     }
                     const zwsAfter = this._insertLinkZws('after', link);
                     if (!zwsAfter.parentElement || !zwsAfter.parentElement.isContentEditable) {
+                        this.observerUnactive('_setLinkZws_zwsAfter_remove');
                         zwsAfter.remove();
+                        this.observerActive('_setLinkZws_zwsAfter_remove');
                     }
                 }
             }

addons/website/static/tests/tours/website_no_dirty_page.js

@@ -69,5 +69,15 @@ wTourUtils.registerWebsitePreviewTour('website_no_dirty_page', {
         content: "Make sure the paragraph still acts as a default paragraph",
         trigger: 'iframe .s_text_image h2 + p.o_default_snippet_text',
         run: () => null,
+    }, {
+        content: "Click on button",
+        trigger: 'iframe .s_text_image .btn',
+        run: function (actions) {
+            actions.click();
+            const el = this.$anchor[0];
+            const sel = el.ownerDocument.getSelection();
+            sel.collapse(el, 0);
+            el.focus();
+        },
     },
 ]));