Fixed the help documentation launch link when the plot is a superplot

[RabiyaF]

Description of work

Closes #38044 .

To test:

1. Create a workspace ws = CreateSampleWorkspace()
2. Open a Superplot

3. Click Help

4. Verify that the help page that opens is the documentation for Superplot.

5. Unclick Superplot

6. Click Help

7. Verify that the help page that opens is the documentation for Basic 1D and Tiled Plots.

---

Reviewer

Your comments will be used as part of the gatekeeper process. Comment clearly on what you have checked and tested during your review. Provide an audit trail for any changes requested.

As per the review guidelines:

• Is the code of an acceptable quality? (Code standards/GUI standards)
• Has a thorough functional test been performed? Do the changes handle unexpected input/situations?
• Are appropriately scoped unit and/or system tests provided?
• Do the release notes conform to the guidelines and describe the changes appropriately?
• Has the relevant (user and developer) documentation been added/updated?
• If the PR author isn’t in the mantid-developers or mantid-contributors teams, add a review comment rerun ci to authorize/rerun the CI

Gatekeeper

As per the gatekeeping guidelines:

• Has a thorough first line review been conducted, including functional testing?
• At a high-level, is the code quality sufficient?
• Are the base, milestone and labels correct?

[Copilot]

Pull request overview

Fixes Workbench plot Help button routing so that when the Superplot mode is active the Help action opens the Superplot documentation (per #38044), otherwise it continues to open the standard plotting help.

Changes:

• Add FigureType.Superplot and map it to the workbench/superplot.html documentation page.
• Route the Help button action to a Superplot-specific handler when the Superplot toggle is checked.
• Add a release note entry describing the corrected documentation link.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
qt/python/mantidqt/mantidqt/plotting/figuretype.py	Adds a FigureType enum entry for Superplot.
qt/applications/workbench/workbench/plotting/toolbar.py	Emits a different signal from Help when Superplot is toggled on.
qt/applications/workbench/workbench/plotting/plothelppages.py	Adds Superplot help URL and a superplot flag to select it.
qt/applications/workbench/workbench/plotting/figuremanager.py	Connects the new toolbar signal to a Superplot help launcher.
docs/source/release/v6.16.0/Workbench/Bugfixes/38044.rst	Release note for the Superplot help link fix.

---

You can also share your feedback on Copilot code review. Take the survey.

[jclarkeSTFC]

It's works well, but I think the comments from Copilot are worth addressing

[jclarkeSTFC]

Thanks for making those changes