Fix for colourbar plot bug

[jhaigh0]

Purpose of work
Fix for bug (introduced in #35195) where if you opened and applied plot setting on a colourfill (or contour) plot, the colour bar positioning would not be recognised, and the plot would draw underneath it.

Summary of work
Reverted my complicated changes required for using a tight layout and a colour bar. Now you can pass a layout engine to create_subplots() to allow the use of a constrained layout for plots with a colour bar. This is what's recommended.

Also altered some tests to make sense with the changes.

To test:

• Load 164198.nxs, 164199.nxs, 164200.nxs and group them together.

• Expand the group and plot a colourfill plot for 164198.nxs

• As you resize the window, no text should become obscured and the plot should behave as expected

• Open the plot settings (settings icon on the toolbar), change nothing, and click 'Apply'.

• Nothing on the plot should change (apart from some very minor adjustments potentially).

• Open the plot settings and change some settings (colour bar and axes limits and scales etc.)

• The plot should update according to your changes

• Now right-click the workspace group and plot a colourfill for all three workspaces.

• Repeat the checks from before.

• Also experiment with contour plots (they should be the same)

• Check that other plot types have not been affected

There is no associated issue.

This does not require release notes because the functionality is covered by the original release note in #35195

---

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?
• Are the release notes saved in a separate file, using Issue or PR number for file name and in the correct location?

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.

[eurydice76]

Thanks for the work done for solving this regression.
I could apply the workflow designed for testing the fix and functionnally
everything seems OK.
The code by itself is OK for me.

[eurydice76]

The build is OK. Could another gatekeeper validate it ? Thanks

[sf1919]

@mantidproject/gatekeepers Adding a screenshot to show that this has passed all its tests and has been approved so ready for gatekeeper review that @eurydice76 has requested