Create the requested number of bins in bin2d_breaks()

[thomasp85]

Fix #3824

This PR fixes the reported bug by removing the last bin if it lies completely outside the the scale range

[yutannihilation]

Looks good.

devtools::load_all("~/repo/ggplot2")
#> ℹ Loading ggplot2

x <- seq(0, 1, length = 1e4)
y <- x + rnorm(length(x))
dt <- data.frame(x, y)

# NOT OK
ggplot(dt, aes(x, y)) +
  geom_point(colour = "grey80") +
  stat_summary_bin(fun = mean, bins = 10, geom = "point", colour = "red")

^{Created on 2021-04-20 by the reprex package (v2.0.0)}