Option to always cancel with right-click

In my use case, I sometimes press right mouse button to cancel selection. In these cases, it sometimes works, but sometimes I accidentally move the mouse by a pixel or two when doing so, and my attempt to cancel still turns into a selection.

It also appears to be impossible to cancel with right-click when predefined rectangles are provided; it just picks the one under the selection.

I'd love to be able to make any usage of right mouse button always cancel selection.

Start by tracing how right-click is handled during selection, including when the pointer moves slightly and when predefined rectangles are available. Implement the requested consistent cancellation behavior, then verify that right-click never selects a rectangle and always cancels the selection.

Written by the indexing model from the issue text.