The sizers which should be adjusted.
The index of the sizer to grow.
The amount to adjust the sizer, positive or negative.
This will adjust the indicated sizer by the specified amount, along with the sizes of the appropriate neighbors, subject to the limits specified by each of the sizers.
This is useful when implementing box layouts where the boundaries between the sizers are interactively adjustable by the user.
Adjust a sizer by a delta and update its neighbors accordingly.