Reviewed and refactored additional editor draft save warnings

- Added testing to cover warning cases.
- Refactored logic to be simpler and move much of the business out of
  the controller.
- Added new message that's more suitable to the case this was handling.
- For detecting an outdated draft, checked the draft created_at time
  instead of updated_at to better fit the scenario being checked.
- Updated some method types to align with those potentially being used
  in the logic of the code.
- Added a cache of shown messages on the front-end to prevent them
  re-showing on every save during the session, even if dismissed.

resources/js/components/page-editor.js

@@ -40,6 +40,7 @@ class PageEditor {
             frequency: 30000,
             last: 0,
         };
+        this.shownWarningsCache = new Set();
 
         if (this.pageId !== 0 && this.draftsEnabled) {
             window.setTimeout(() => {
@@ -119,8 +120,9 @@ class PageEditor {
             }
             this.draftNotifyChange(`${resp.data.message} ${Dates.utcTimeStampToLocalTime(resp.data.timestamp)}`);
             this.autoSave.last = Date.now();
-            if (resp.data.warning.length > 0) {
+            if (resp.data.warning && !this.shownWarningsCache.has(resp.data.warning)) {
                 window.$events.emit('warning', resp.data.warning);
+                this.shownWarningsCache.add(resp.data.warning);
             }
         } catch (err) {
             // Save the editor content in LocalStorage as a last resort, just in case.