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 pltimport numpy as npx = np.linspace(-5, 5, 1000)y = x ** 2fig = 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_coordax1.plot(x, y)plt.show()

Before:

After:

PR Checklist

• Has Pytest style unit tests
• Code isFlake 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