Add support for inline diff in content editor

What does this MR do?

Issue: #338272 (closed)

Adds support for rendering inline diff marks in content editor.

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

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

1. {+added content+}
1. {-removed content-}

3. Click "Use new editor".

4. The content editor will automatically convert the elements to inline diff marks.

   [You can also insert inline diff directly in the content editor as shown in the gif above.]

5. 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 #338272 (closed)