Refactor the Stretch tab in BayesFitting to meet MVP design pattern

[MohamedAlmaki]

Description of work

This pull request replaces the old single-class Stretch tab with new model, presenter, and view classes to follow the MVP pattern. The goal of this work is to modernize the current codebase of the tab and adhere to best design practices.
Fixes #38005.

To test:

Follow the manual testing documentation and try to test multiple scenarios: https://developer.mantidproject.org/Testing/Inelastic/BayesFittingTests.html

---

Reviewer

Please comment on the points listed below (full description).
Your comments will be used as part of the gatekeeper process, so please comment clearly on what you have checked during your review. If changes are made to the PR during the review process then your final comment will be the most important for gatekeepers. In this comment you should make it clear why any earlier review is still valid, or confirm that all requested changes have been addressed.

Code Review

• Is the code of an acceptable quality?
• Does the code conform to the coding standards?
• Are the unit tests small and test the class in isolation?
• If there is GUI work does it follow the GUI standards?
• If there are changes in the release notes then do they describe the changes appropriately?
• Do the release notes conform to the release notes guide?

Functional Tests

• Do changes function as described? Add comments below that describe the tests performed?
• Do the changes handle unexpected situations, e.g. bad input?
• Has the relevant (user and developer) documentation been added/updated?

Does everything look good? Mark the review as Approve. A member of @mantidproject/gatekeepers will take care of it.

Gatekeeper

If you need to request changes to a PR then please add a comment and set the review status to "Request changes". This will stop the PR from showing up in the list for other gatekeepers.

[robertapplin]

Thanks for this much needed refactor! I've done a first pass through the code and have a couple of suggestions below

Please can you also add a test for the presenter and model?

[robertapplin]

Thanks for your changes, I have a few more minor suggestions then I'm happy to approve!

[robertapplin]

This is working well, I have followed the manual testing instructions and it is working as expected. The only thing I noticed, is the options in the table are now non-editable, whereas it used to be possible to click in these table cells and change their value

[MohamedAlmaki]

Fixed, it should work now

[robertapplin]

Thanks for the changes, this looks good to go 👍