Recently, numpy#29112 added showing first mismatches indices, but
assert_array_almost_equal.compare trips it up by returning a shape
different from its input, causing an IndexError:

```
    <...>
    if invalids.ndim != 0:
        if flagged.ndim > 0:
>           positions = np.argwhere(np.asarray(~flagged))[invalids]
E           IndexError: boolean index did not match indexed array along axis 0; size of axis is 3 but size of corresponding boolean axis is 2
```
(traceback shown using pytest --full-trace)

A nice cleanup (newer, similar inf handling already exists now in
assert_array_compare), and resolves the shape mismatch issue. However,
the removed logic was handling complex infs while the one isn't, causing
the new test and an existing one (TestInterp::test_complex_interp) to
now fail with RuntimeWarnings attempting to subtract the complex infs.

assert_array_compare now tests all inf values for matching position
and value, including complex infs.

Fixes the failing tests.

The behavior for real infs is the same is before.

For complex infs, demonstrates that the behavior for mismatching
values is now cleaner, showing a concise error message vs.
previously displaying nan max errors.

For complex infs with matching values, the behavior is the same as
before, accepting them as equal (although internally they would
now be filtered ahead of being passed to isclose, like real infs
already had been).