BUG: symlog colorbar with linear threshold < vmin + matplotlib 3.5

[neutrinoceros]

Bug report

Bug summary

Code for reproduction

import matplotlib
import numpy as np
import yt

prng = np.random.RandomState(0)
d = {'my_fake_density': prng.random_integers(1, 3, size=(64,64,64))}

ds = yt.load_uniform_grid(d, [64,64,64])
p = yt.SlicePlot(ds, "z", ('stream', 'my_fake_density'))
p.set_log(('stream', 'my_fake_density'), True, linthresh=1.e-3)
p.save(f"/tmp/mpl_{matplotlib.__version__}_")

Actual outcome

Expected outcome
This is the result of the same script, using matplotlib 3.4.3

Arguably, the behaviour with MPL 3.4 can be considered canonical, but maybe we need to add a warning when the value of linthresh is under the actual minimum value.

I note that this reference behaviour, setting the lower limit of the colobar to the data's minimum rather than the user required linthresh, is in line with what can be obtained in both matplotlib 3.4 and 3.5 without yt:

import matplotlib.pyplot as plt
from matplotlib.colors import SymLogNorm
import matplotlib
import numpy as np

prng = np.random.RandomState(0)
data = prng.random_integers(1, 3, size=(64,64))

fig, ax = plt.subplots()
im = ax.imshow(data, norm=SymLogNorm(linthresh=1e-2))
cb = fig.colorbar(im)
file = f"/tmp/threshold_mpl_{matplotlib.__version__}.png"
fig.savefig(file)

gives

[neutrinoceros]

The fix is likely along the lines of preventing the norm class to be set to SymLogNorm when it doesn't make sense, do it as early as possible, and emit a warning.
I'll give it a go later