Figure.histogram: Migrate parameter 'stairs' to the new alias system

[seisman]

This PR migrates the stairs parameter (option -S) to the new alias system.

Over the past few days, I considered whether we should adopt Matplotlib's design (https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.hist.html), which exposes a histtype parameter accepting values "bars", "stepfilled", "step", and "barstacked" (but we already alias histtype to -Z). Matplotlib also provides an example demonstrating these histogram styles at https://matplotlib.org/stable/gallery/statistics/histogram_histtypes.html.

It turns out GMT is more flexible: it can reproduce Matplotlib’s various histogram types via different combinations of pen, fill, and stairs, as illustrated below. Thus, this PR is simply a routine parameter migration.

import numpy as np
import pygmt
from pygmt.params import Axis, Frame

# Generate random elevation data from a normal distribution
rng = np.random.default_rng(seed=100)
mean = 100  # mean of distribution
stddev = 25  # standard deviation of distribution
data = rng.normal(loc=mean, scale=stddev, size=521)

fig = pygmt.Figure()
fig.histogram(data=data, frame=Frame(axes="WSen", title="bars"), series=5, fill="green")
fig.shift_origin(xshift="w+1")
fig.histogram(data=data, frame=Frame(axes="WSen", title="bars"), series=5, fill="green", pen="1p")

fig.shift_origin(xshift="w+1")
fig.histogram(data=data, frame=Frame(axes="WSen", title="step"), series=5, stairs=True, pen="1p")

fig.shift_origin(xshift="w+1")
fig.histogram(data=data, frame=Frame(axes="WSen", title="stepfilled"), series=5, stairs=True, pen="2p", fill="green")

fig.show()

Related: I feel we should add this image showing different types of histograms that GMT can provide. We already have a tutorial at https://www.pygmt.org/dev/tutorials/advanced/cartesian_histograms.html, which shows several histograms, but only one is shown in the API page (https://www.pygmt.org/dev/api/generated/pygmt.Figure.histogram.html#pygmt.Figure.histogram). Maybe we should add a separate gallery example instead?