Code Modernization: Introduce the spread operator in `WP_HTTP_IXR_Client`.

Rather than relying `func_get_args()` to retrieve arbitrary function arguments, we can now use the spread operator to assign them directly to a variable.

This makes the signature of `WP_HTTP_IXR_Client::query()` compatible with the parent class method.

Follow-up to [48204].

Props ayeshrajans.
See #48267, #47678.
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