TST: Move new asarray test to a more appropriate place. (#22251)

As noted at #21995 (comment), the new test from #21995 was placed in a directory intended for the Array API, and unrelated to the change.

* Consolidate test_dtype_identity into an existing test file.

Remove `test_asarray.py`. Create a new `TestAsArray` suite in
`test_array_coercion.py`

* Linting.

Wrap some comments that got too long after function became
a method (with additional indentation).

Original NumPy Commit: 4d4fca0cef2e5594a50c1d10a9db6f21aaba0a58

Author: eirrgang