In many graphics apps, holding Ctrl and/or Shift locks the ratio of
the rectangle being resized, making it quicker than manually choosing
a ratio. This patch adds this functionality to the Crop tool.
When Ctrl or Shift is pressed, the current ratio of the crop rect
is saved, "locking it". When resizing, so long as Ctrl or Shift is
pressed, the ratio is enforced to this locked value. Otherwise it
behaves the same as before - enforcing ratio if one was chosen in
Depends on D11379