Fix #2320 Split geometry visual problems

[ValentinBuira]

This PR fix #2320 where the guideline from last point to cursor wasn't showing in the splitting tool

The root issue was that the GuidelineController::buildGuideline was cancelled at the beginning of the function, because of the allowed property. So I turned allowed to be always true for the splitting tool

I wanted to show clearly to the users that the actual splitting line were the one to the last point and not to the cursor.
So I updated the visual to match the way it works when adding a new line geometry
Let me know if it's working for the user experience otherwise I will revert that part

[github-actions]

Pull Request Test Coverage Report for Build 10215399786

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 5 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.03%) to 59.991%

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Files with Coverage Reduction	New Missed Lines	%
input/app/projectsmodel.cpp	5	69.44%

Totals
Change from base Build 10161670477:	-0.03%
Covered Lines:	7701
Relevant Lines:	12837

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💛 - Coveralls

[tomasMizera]

The code is looking good, I have just one suggestion. The first recorded point for the split line has a different color than the line. Can we unify that please?

[ValentinBuira]

I changed the marker color to match the color of the line

Should be ready to merge once unfrozen