Support dask objects as indexers for `dask.array.Array.vindex`

[gcaria]

This came from a discussion in #8928, where this message from @jsignell contains useful hints on how to start working on this.

[gcaria]

I wanted to have a look at this, but I see that simply commenting out this elif on main returns a dask array in this MRE:

import dask.array as da
import numpy as np

x = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
x = da.from_array(x, chunks=2)
y = da.from_array([0, 1, 2], chunks=2)

out = x.vindex[[0, 1, 2], [0, 1, 2]]
out = x.vindex[y, y]
type(out) # dask.array.core.Array