Add support for task lists in content editor

What does this MR do?

Issue: #338269 (closed), Also fixes #335970 (closed)

Add support for task lists (regular tasks lists and numeric task lists) in content editor

For example:

• regular task list item

1. numeric task list item

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

1. Edit a Wiki page.
2. Type the below code:

* [x] hello
  * [x] world
  * [ ] example
    * [ ] of nested
      * [x] task list
      * [ ] items


1. [x] hello
2. [x] world
3. [ ] example
   1. [ ] hello
   2. [ ] world
4. [x] task list
5. [ ] items

1. Click "Use new editor".
2. The Content Editor will convert the text into a task lists / numeric task lists.
3. Click "save". The content should be saved successfully.

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Related to #338269 (closed)