Pack an OperationCanceledException inside the InterruptedException when
this is thrown due to the user canceling an operation. This makes it
easier to determine the cause of the InterruptedException from outside
the methods (i.e. in the catch-clauses). Adapt the method
ModalContext::checkCanceled accordingly. Change
WorkspaceModifyOperation::run so it preserves the original
exceptions if possible.

Same idea as
https://github.com/eclipse-platform/eclipse.platform.ui/pull/1259