new margin system doesn't handle negative values in bars #7175
Description
While working on #5538 (comment) (allow artists to opt-out from being considered by the autoscaler), I noticed that the new margins machinery doesn't handle negative values in bar plots very well:
from matplotlib import pyplot as plt
fig, axs = plt.subplots(1, 2)
# wanted behavior: remove the margin at y=0.
axs[0].bar(0, 1)
# unwanted behavior: remove the margin at y=-1
axs[1].bar(0, -1)
plt.show()
attn @mdboom