Address some GUI issues on the field calculator

 * Info labels for edit mode turn on was not shown
 * Ok button was active when opening the field calculator even with no input (Fix #11403)
Field calculator: Move virtual field to the top.

Followup 0c4a501
use qIsNaN instead of isnan (fixes windows build)
[composer] Fix incorrect calculation of frame thickness for labels

Previously entire frame width was considered when calculating
the margin for the label item. Only half the frame width should be
used, since half is drawn outside the item rect.
[FEATURE][composer] Allow control of hoz and vert margins for labels

Previously only a single margin setting would apply to both
horizontal and vertical margins. This change allows users to specify
different horizontal and vertical margins.
[FEATURE][composer] Allow negative margins for label items

If negative margins are set for a label, the label contents will
begin outside the bounds of the label. This is desirable for
aligning label items with other items while allowing for optical
margin alignment for the label type.
[FEATURE][composer] Add view menu option to hide bounding boxes

This allows users to hide the bounding boxes for selected items
within a composition. It's a handy feature for allowing interaction
with items while previewing exactly how they will look when the
composition is exported, without large boxes blocking the view.