Promote isclose arguments to inexact dtype (fixes #19935).

[tillahoffmann]

It turns out that #19935 is easily fixed by promoting to inexact dtypes. This ensures np.isclose(6, 10, rtol=0.5) and jnp.isclose(6, 10, rtol=0.5) give the same result.

[jakevdp]

Looks great, thanks!

[jakevdp]

This is causing some downstream test failures for isclose called on key types:

import jax
key = jax.random.key(0)
jax.numpy.isclose(key, key)

We should probably fall back to equality checks when the following is true dtypes.issubdtype(dtype, dtypes.extended).

[jakevdp]

Thanks!

Last thing - could you squash your changes into a single commit please? See https://jax.readthedocs.io/en/latest/contributing.html#single-change-commits-and-pull-requests