`polyval` returns objects with different dimension order

[malmans2]

What is your issue?

I noticed that the dimension order of the object returned by the latest polyval (main, unreleased) is different compared to xarray<=2022.3.0.
For example, the following code returns different results.

import xarray as xr
import numpy as np

values = np.array(
    [
        "2021-04-01T05:25:19.000000000",
        "2021-04-01T05:25:29.000000000",
        "2021-04-01T05:25:39.000000000",
        "2021-04-01T05:25:49.000000000",
        "2021-04-01T05:25:59.000000000",
        "2021-04-01T05:26:09.000000000",
    ],
    dtype="datetime64[ns]",
)
azimuth_time = xr.DataArray(
    values, name="azimuth_time", coords={"azimuth_time": values - values[0]}
)

polyfit_coefficients = xr.DataArray(
    [
        [2.33333335e-43, 1.62499999e-43, 2.79166678e-43],
        [-1.15316667e-30, 1.49518518e-31, 9.08833333e-31],
        [-2.50272583e-18, -1.23851062e-18, -2.99098229e-18],
        [5.83965193e-06, -1.53321770e-07, -4.84640242e-06],
        [4.44739216e06, 1.45053974e06, 5.29960857e06],
    ],
    dims=("degree", "axis"),
    coords={"axis": [0, 1, 2], "degree": [4, 3, 2, 1, 0]},
)

ds_out = xr.polyval(azimuth_time.coords["azimuth_time"], polyfit_coefficients)
print(ds_out.dims)

xarray v2022.3.0
('azimuth_time', 'axis')

xarray v2022.3.1.dev103+gfc282d59
('axis', 'azimuth_time')

Is this the expected behaviour? If yes, is it worth mentioning this change in what's new/breaking changes?

cc: @headtr1ck

[headtr1ck]

Would be easily fixable by changing:

res = coeffs.isel({degree_dim: max_deg}, drop=True) + zeros_like(coord)

to

res = zeros_like(coord) + coeffs.isel({degree_dim: max_deg}, drop=True)

At least until broadcasting rules don't change.

[headtr1ck]

The old behavior is closer to numpy, so I guess worth fixing.