Add ability to delete task list items

What does this MR do and why?

This MR adds the ability to delete task list items.

It adds an ellipsis dropdown next to each task list item in an issue description to allow the user to delete the task list item. Any sub-task list items remain and are moved up a nested level.

Behind feature flag work_items_create_from_markdown default disabled, so no changelog required.

Issue: #377307 (closed)

The next MR will add the ability to convert the task list item to a Task.

Screenshots or screen recordings

Screen_Recording_2023-01-11_at_6.28.09_pm

Old screencasts

Commit 1: Screen_Recording_2023-01-10_at_1.47.54_pm

How to set up and validate locally

1. In rails console enable the feature flag

   Feature.enable(:work_items_create_from_markdown)

2. Visit any issue such as http://127.0.0.1:3000/h5bp/html5-boilerplate/-/issues/1
3. Create task list items in the description
4. Test using the ellipsis dropdown to delete the task list item

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #377307 (closed)

app/assets/javascripts/issues/show/components/description.vue

@@ -98,6 +98,7 @@ export default {
     const workItemId = getParameterByName('work_item_id');
 
     return {
+      hasTaskListItemActions: false,
       preAnimation: false,
       pulseAnimation: false,
       initialUpdate: true,
@@ -367,6 +368,7 @@ export default {
 
         this.addPointerEventListeners(item, '.task-list-item-actions');
         this.insertNextToTaskListItemText(this.createTaskListItemActions(), item);
+        this.hasTaskListItemActions = true;
       });
     },
     addHoverListeners(taskLink, id) {
@@ -491,6 +493,7 @@ export default {
       :class="{
         'issue-realtime-pre-pulse': preAnimation,
         'issue-realtime-trigger-pulse': pulseAnimation,
+        'has-task-list-item-actions': hasTaskListItemActions,
       }"
       class="md"
     ></div>