Fix issue with drawing 3D lines where points are from nparray

[oscargus]

PR Summary

Closes #23459

The dimensions were different since get_xdata and get_ydata have processed the return values. So do a similar processing here.

PR Checklist

Tests and Styling

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

• [N/A] New features are documented, with examples if plot related.
• [N/A] New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• [N/A] API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).
• [N/A] Documentation is sphinx and numpydoc compliant (the docs should build without error).

[QuLogic]

A far clearer test is:

fig = plt.figure()
ax = fig.add_subplot(projection='3d')

ax.plot([[0], [1]], [[0], [1]], [[0], [1]])

which clearly shows that we seem to be downcasting 2D if its shape is (N, 1) to 1D with shape (N, ). I'm surprised that this works in 2D, but 2D plot accepts a bunch of weird things, so I guess we need to allow it in 3D.

[oscargus]

Ahh, I didn't fully get the reason behind the error. Much clearer test suggested indeed.