Breaking change in 3.2: quiver.set_UVC does not support single numbers any more

[maxnoe]

Bug report

Bug summary

In prior versions of matplotlib, it was possible to set all UVC values to the same by calling quiver.set_UVC with single numbers for U and V. This raises an error in matplotlib 3.2.

Code for reproduction

import matplotlib.pyplot as plt

q = plt.quiver(
    [0, 0, 1],
    [0, 1, 1],
    [0.5, 0.5, 0.5],
    [0, 0, 0],
)

q.set_UVC(0, 0.5)
plt.xlim(-1, 2)
plt.ylim(-1, 2)
plt.show()

Actual outcome

matplotlib 3.1 works as expected, matplotlib 3.2 raises:

    q.set_UVC(0, 0.5)
  File "/home/maxnoe/.local/anaconda3/lib/python3.7/site-packages/matplotlib/quiver.py", line 604, in set_UVC
    raise ValueError(f'Argument {name} has a size {var.size}'
ValueError: Argument U has a size 1 which does not match 3, the number of arrow positions

Expected outcome

No breaking changes between minor revisions.

[tacaswell]

Sorry about that!