[FIX] web_editor: notify current step when joining a collaborator which already synced

How to reproduce (scenario):
- Open 3 windows with 3 different sessions in Odoo
user_1 -> in CRM, My Pipeline
user_2 -> in Knowledge on article "target"
user_3 -> in Knowledge on article "target"
-> user_2 and user_3 are in a collaborative session
-> user_1 "insert view in article" "target" (via Favorites)
-> user_1 is redirected to knowledge to the target article
-> RTC_DATA_CHANNEL_OPEN between user_1 and user_2 happens
-> user_1 reset the html_field value from the history steps of user_2
-> the embedded view "My Pipeline" is inserted via `execCommand` and create a
step in user_1 editor
-> user_2 is notified via OE_HISTORY_STEP and receive the new nodes (view)
-> RTC_DATA_CHANNEL_OPEN between user_1 and user_3 happens
-> since user_3 was already synced with user_2, there is no
`historyResetFromSteps`
-> user_3 does not get the step from user_1 with the embedded view nodes now
-> user_3 makes multiple steps (i.e. write some text in a paragraph)

Current Behavior:
-> user_2 and user_1 are notified of those steps and add them to their histories
-> user_3 stil did not get the step with the embedded view nodes
-> now if user_1 and user_2 make some steps, user_3 will be notified, but those
steps "parents" are the steps from user_3, so user_3 may not request a full
history comparison and may never get the missing step

Fix:
-> when a RTC_DATA_CHANNEL_OPEN event happens, the connected client is notified
of the last registered step so it can call GET_MISSING_STEPS if it does not have
it

Note:
This fix solves the specific case mentioned above, but other cases of
desynchronization may happen, see Task-3208277 for a more complete fix.

Task-2821374

Part-of: odoo/odoo#104680

addons/web_editor/static/src/js/wysiwyg/wysiwyg.js

@@ -566,10 +566,12 @@ const Wysiwyg = Widget.extend({
                                 }
                                 historySyncFinished = true;
                             } else {
+                                const currentStep = this.odooEditor._historySteps[this.odooEditor._historySteps.length - 1];
                                 const remoteSelection = await this.ptp.requestClient(fromClientId, 'get_collaborative_selection', undefined, { transport: 'rtc' });
                                 if (remoteSelection) {
                                     this.odooEditor.onExternalMultiselectionUpdate(remoteSelection);
                                 }
+                                this.ptp.notifyClient(fromClientId, 'oe_history_step', currentStep, { transport: 'rtc' });
                             }
                             break;
                         }