Design widget - Enable commenting

What does this MR do and why?

Enabled adding comments in design view for work item's Design widget!

NOTE TO REVIEWER

I do apologize for the bloated size of this MR, but I do believe that the ability to test the functionality in one go would be more beneficial and efficient. The functionality is completely identical to the legacy experience, with code having very minor updates here and there. Please refer to the instructions on testing below for the ease of mind!

Please also note that moving of the pins on the design functionality is not a part of this MR.

Known bug

Please note that I have noticed a certain bug when deleting a comment:

If the comment has a thread associated with it, and the comment being deleted is the main thread (a top level comment), the entire pin is not being removed and the Thread count is not being updated (this applies for both the Unresolved and Resolved sections). The main comment is deleted, but the next comment in the thread is moved up to its place now. This is not ideal, however, this behaviour is replicated from the legacy experience. So I suggest tackling this bug separately and have created an issue for it: #505188

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After
	Screen_Recording_2024-11-18_at_9.25.56_PM

How to set up and validate locally

To efficiently tests all edge cases of the flow, please follow along the acceptance criteria checklist provided in the MR's issue 😊

Related to #462952 (closed)