Allow the Trim/Extend Tool to keep the reference line for multiple trim/extend actions

[YoannQDQ]

• Fix Allow the Trim/Extend Tool to keep the reference line for multiple trim/extend actions #59634

Description

Pressing Ctrl or Shift while trimming/extending a feature now keeps the reference feature.
Also fix the rubber band display when the layer crs != canvas crs.

[github-actions]

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[baswein]

Thanks for this amazing upgrade!

I just added a couple of semi related feature requests.
One that asks for an infinite line rubber band. #59683
In my ignorance I imagine this would be fairly straight forward as we already do it in a lot of places in QGIS.
And a much more involved one that suggests the ability to select multiple target segments.
#59685
While that feature is a long shot it would likely require either the ctrl or shift key to be used and it seems that you are utilizing both of them for this feature which makes me think we should reserve one of them for future features and options.

Also I think we should upgrade the tool tip help text to identify the modifier and that segment snapping is required to use the tool.
I'm happy to do that as a separate pull request as it is within my limited capabilities.

[lbartoletti]

Wonderful! I'd never taken the time to do that, and yet it was just a few lines of code! Many thanks.
Please can you add tests?

[qgis-bot]

@YoannQDQ
This pull request has been tagged as requiring documentation.

A documentation ticket will be opened at https://github.com/qgis/QGIS-Documentation when this PR is merged.

Please update the description (not the comments) with helpful description and screenshot to help the work from documentors.
Also, any commit having [needs-doc] or [Needs Documentation] in will see its message pushed to the issue, so please be as verbose as you can.

Thank you!

[lbartoletti]

You have to cas to an integer. I guess, that you could replace std::round by static_cast.