Add Figure.fill_between to fill between two curves

[seisman]

This PR provides an initial implementation for the Figure.fill_between method, which fills the area between two curves.

The two curves are called y1 and y2 in the docstring. Curve y1 is specified via x/y, and curve 2 is specified via x/y2. Therefore, the two curves must be co-registered. Supporting for curves that are not co-registered can be done by adding a separate parameter x2, which can be done in a future PR.

This PR mainly wraps the plot's -M option. Core options include:

• -W: pen
• -G: fill
• -l: label
• -M
  • c: y1 and y2 are co-registered
  • s: y1 and y2 are not co-registered [not supported yet]
  • +g: fill2 fill for y2>y1
  • +l: label2 label for y2 curve
  • +p: pen2 pen for y2 curve
  • +r: draw legend entries as lines, rather than filled boxes [it may contains bugs]
  • +y: y2 is a horizontal constant, i.e., y2=0

An working example

import numpy as np
import pygmt

x = np.linspace(0, 2 * np.pi, 200)
fig = pygmt.Figure()
fig.fill_between(
    x=x,
    y=np.sin(2 * x),
    y2=np.sin(3 * x),
    region=[0, 2 * np.pi, -1.2, 1.2],
    projection="X10c/4c",
    frame=True,
    fill="lightblue",
    pen="1p,blue",
    fill2="lightred",
    pen2="1p,red",
)
fig.show()

Address #4678

Preview: https://pygmt-dev--4679.org.readthedocs.build/en/4679/api/generated/pygmt.Figure.fill_between.html

[github-actions]

Summary of changed images

This is an auto-generated report of images that have changed on the DVC remote

Status	Path
added	pygmt/tests/baseline/test_fill_between_two_coregistered_curves.png
added	pygmt/tests/baseline/test_fill_between_y2_scalar.png

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Details

Added images

• test_fill_between_two_coregistered_curves.png

• test_fill_between_y2_scalar.png

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Report last updated at commit f555308