This is a simple helper that returns the number of pages it takes to plot all
panels when using facet_wrap_paginate
. It partially builds the plot so depending
on the complexity of your plot it might take some time to calculate...
n_pages(plot)
If the plot uses using either facet_wrap_paginate or facet_grid_paginate it returns the total number of pages. Otherwise it returns NULL
A ggplot object using either facet_wrap_paginate or facet_grid_paginate