spatial resample -- adaptive padding mode when switching the backends

[wyli]

for the array pad functions there's numpy->torch mode str adaptation

MONAI/monai/transforms/croppad/functional.py

Lines 41 to 43 in 554b172

	def _convert_pt_pad_mode(padding_mode):
	"""get the most similar mode of `pad` from ``padding_mode`` of the spatial resampling."""
	if padding_mode is None or padding_mode in ("zeros", "constant", "grid-constant"):

would be great to implement the same idea for spatial resampling

MONAI/monai/transforms/spatial/array.py

Lines 1818 to 1821 in 554b172

	def resolve_modes(interp_mode, padding_mode):
	"""compute the backend and the corresponding mode for the given interpolation mode and padding mode."""
	_interp_mode = None
	_padding_mode = None

[atbenmurray]

@wyli This is the second PR I want to make to #5860

It should be ready later today. It is a bit more involved than just this because whether you can map or not is also dependent on the way that you are going to resample.