Adjust clicking area for x labels

[lee1043]

This is part of plot, for x-axis label, clicking area (in grey) is pretty wide to below and above the label itself, which the above part overlaps with the portrait plot itself. I need to shorten the clicking area, can you give a hint where should I start?

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Comments from @doutriaux1:

vcs gettextextent
the function above is what is ued to determine the box length. Ask Carlos and Dan Lipsa, it comes back from VTK
gettextextent calls VTK
then we convert that to vcs's x/y . And then these to png dims
The last part works for sure
You can ask Carlos to check that what we get from VTK is converted correctly to VCS' x/y coordinatinates
if that's correct ask Dan to check the our call to VTK is correct and that there's no bug in VTK

I do believe we have a test in the test suite for this. Ask Paul and Carlos if they remember which testit is