PR: Implement mouse XButton navigation in the editor

[maurerle]

Description of Changes

• Wrote at least one-line docstrings (for any new functions)
• Added unit test(s) covering the changes (if testable)

• Included a screenshot or animation (if affecting the UI, see Licecap)

I added navigation with XButtons (the typical extra two buttons on a mouse used for browsing backward and forward) in the code editor.
This improves code browsing if the mouse has this ability.

I don't know if this is testable and how, as it only adds a new trigger which is forwarded to the one in the EditorStack.

Issue(s) Resolved

Fixes #15948

Affirmation

By submitting this Pull Request or typing my (user)name below,
I affirm the Developer Certificate of Origin
with respect to all commits and content included in this PR,
and understand I am releasing the same under Spyder's MIT (Expat) license.

I certify the above statement is true and correct: Florian Maurer

[ccordoba12]

Hey @maurerle, thanks a lot for your contribution! To have it in one of the next releases in the Spyder 5 cycle, please make your branch to derive from our 5.x one (instead of master), with the following commands:

git checkout 5.x
git checkout feature/xbutton
git rebase --onto 5.x master feature/xbutton
git push -f origin feature/xbutton

You need to do the same for the other pull requests that you opened today. More details about our development process are available in our Contributing guide.

[maurerle]

Thank you!
I updated all my contributions. Could you please review them and give feedback?

[ccordoba12]

I don't have much free time these days, but I'll ask @dalthviz (one of our core developers) to take a look at them.

[dalthviz]

Thank you @maurerle for this! Checked locally and is working. Quite nice improvement in the navigation experience if you have a mouse with extra buttons on the side indeed 👍