Interpolation - Support extrapolation method "clip"

Hello,

I would like an option in da.interp() that instead of returning NaNs during extrapolation returns the data corresponding to the end of the breakpoint data set range.

One way to do this is to limit the new coordinates to the array coordinates minimum and maximum value, I did a simple example with this solution down below.
I think this is a rather safe way as we are just modifying the inputs to all the various interpolation classes that xarray is using at the moment.
But it does look a little weird when printing the extrapolated value, the coordinates shows the limited value instead of the requested coordinates. Maybe this can be handled elegantly somewhere in the source code?

MATLAB uses this quite frequently in their interpolation functions:

• https://mathworks.com/help/simulink/ug/methods-for-estimating-missing-points.html
• https://mathworks.com/help/simulink/slref/2dlookuptable.html

MCVE Code Sample

import numpy as np
import xarray as xr


def interp(da, coords, extrapolation='clip'):
    """
    Linear interpolation that clips the inputs to the coords min and max value.

    Parameters
    ----------
    da : DataArray
        DataArray to interpolate.
    coords : dict
        Coordinates for the interpolated value.
    """
    if extrapolation == 'clip':
        for k, v in da.coords.items():
            coords[k] = np.maximum(coords[k], np.min(v.values))
            coords[k] = np.minimum(coords[k], np.max(v.values))

    return da.interp(coords)


# Create coordinates:
x = np.linspace(1000, 6000, 4)
y = np.linspace(100, 1200, 3)

# Create data:
X = np.meshgrid(*[x, y], indexing='ij')
data = X[0] * X[1]

# Create DataArray:
da = xr.DataArray(data=data, coords=[('x', x), ('y', y)], name='data')

# Attempt to extrapolate:
datai = interp(da, {'x': 7000, 'y': 375})

Expected Output

print(datai)
<xarray.DataArray 'data' ()>
array(2250000.)
Coordinates:
    x        float64 6e+03
    y        float64 375.0

Versions

Start at the da.interp() entry point and reproduce the MCVE with coordinates outside the breakpoint range. Define how a "clip" option should affect extrapolated values while preserving the requested output coordinates, then verify that out-of-range interpolation returns the corresponding endpoint values instead of NaNs.