PR Summary

• adjust the width of messagebox with the window size
• display in two lines properly when its width is not enough for single-line display

closes #16498

Example:

from matplotlib import pyplot as plt
import numpy as np

x = np.linspace(-5, 5, 1000)
y = x ** 2

fig = plt.figure()
ax1 = fig.add_subplot(1, 1, 1)

def my_format_coord(x, y):
    return f'the x-coordinate = {x}, the y-coordinate = {y}'

ax1.format_coord = my_format_coord
ax1.plot(x, y)
plt.show()

Before:

After:

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way