Fix remaining issues with labels

Labels have some remaining issues:

• labelWidth is not updated when font changes (or any property, like size, in font), and labels are not updated accordingly (just calling updateLabels() in if (themeDirtyBits.fontDirty) {...} does not work, as it results in a loop that keeps on updating the labels over and over again for some reason. It takes care of the width, though
  • 447822: Fix issue on scale size of label and font | https://codereview.qt-project.org/c/qt/qtdatavis3d/+/447822
• labelWidth is not taken into account when determining the position of the labels. This results in labels overlapping the graph, if labels are wide enough, and being too far from the graph if the font is small and label narrow
  • 447151: Fix label position adjustment to match with its width | https://codereview.qt-project.org/c/qt/qtdatavis3d/+/447151
• fonts without a border seem to result in a way too small font in labels. Font size seems to be handled in the same way in both cases, so not sure what's causing it
  • 447822: Fix issue on scale size of label and font | https://codereview.qt-project.org/c/qt/qtdatavis3d/+/447822
• label rotations are wrong in some cases. Compare qmlscatter between old and new, as an example-
  • 446249: Label and grid update function is integrated | https://codereview.qt-project.org/c/qt/qtdatavis3d/+/446249
• updateLabels() should be handled in QQuickDataVisItem instead of all graphs individually
  • 446249: Label and grid update function is integrated | https://codereview.qt-project.org/c/qt/qtdatavis3d/+/446249