tool/transform : Can manipulate granularity during cage transform

Summary:
The patch adds a QComboBox to the transform tool options to adjust the
granularity preview while doing cage transforms, it also changes the
QSpinBox to change the real granularity to a QComboBox.

CCBUG:344210

Reviewers: #krita, rempt, dkazakov
Reviewed By: #krita, dkazakov
Subscribers: #krita
Tags: #krita

Differential Revision: https://phabricator.kde.org/D17807