katestatusbar: fix margin in status bar buttons on certain styles

Merged Georg Gadinger requested to merge ggadinger/ktexteditor:fix-new-status-bar-margin into master

On e.g. the Macintosh style the margin for a QPushButton is way larger than with Breeze or Windows. Therefore to prevent cutting off the text, calculate the margin from the style's PM_FocusFrameVMargin (currently this is set to 2 on Breeze, and to 4 on the Macintosh style).

Thanks to @waqar for suggesting the fix!

Merge request reports