Function includeCalleesOfDefinition

For includeCallees: given the id of a function-definition vertex, enqueues the vertex that binds/defines the function (e.g. f <- function..., via the defined-by edge) as well as all of its call sites (via calls edges). Call site arguments are picked up automatically once the call vertex is processed normally, as argument edges are always traversed. This is the reverse of what sliceForCall does for call -> definition linking.