plotting of 2D current collector variables

[rtimms]

Doing sim.plot with a 2D current collector variable doesn't give the correct plot, but also doesn't raise an error. We should either fix it or raise an error.

e.g. doing

options = {
    "current collector": "potential pair",
    "dimensionality": 2,  # 2D current collectors
    "thermal": "x-lumped",
}
model = pybamm.lithium_ion.SPM(options)
sim = pybamm.Simulation(model)
solution = sim.solve()

sim.plot(["Negative current collector potential [V]"])

gives the wrong plot. But

phi_s_cn = solution["Negative current collector potential [V]"]

param = model.default_parameter_values
L_z = param.evaluate(pybamm.standard_parameters_lithium_ion.L_z)
l_y = phi_s_cp.y_sol[-1]  # dimensionless width
l_z = phi_s_cp.z_sol[-1]  # dimensionless height
y_plot = np.linspace(0, l_y, 21) * L_z
z_plot = np.linspace(0, l_z, 21) * L_z
t_plot = 1000

phi_s_cn_plot = plt.pcolormesh(
    y_plot, z_plot, phi_s_cn(y=y_plot, z=z_plot, t=t_plot), shading="gouraud"
)

gives the correct result. The result from sim.plot is transposed, so we just need to catch/fix this in quickplot.