Adjust spacing in crop UI

Summary:
Currently the multitude of labels and spinboxes in the advanced
{nav Crop} bar looks quite cluttered.

By adjusting the horizontal spacing we can group corresponding elements.
This makes the interface slightly faster to navigate and clears up any
ambiguity regarding which labels belong to which spinboxes.

While the minimum horizontal window size while opening the advanced
options will get slightly wider, everything should still fit on a
typical display.

Test Plan:
{nav Crop > Advanced Settings} works as before, looks better. Spacing
still works fine with other widget styles.

Before: {F6202244}
After: {F6202243}

Reviewers: #gwenview, muhlenpfordt

Reviewed By: #gwenview, muhlenpfordt

Subscribers: muhlenpfordt

Differential Revision: https://phabricator.kde.org/D14907