Allow download_url to respect content-disposition header

[cklosows]

In #34938 it was proposed to use a filter in the wp_tempnam function which was rejected in favor of ignore the query string when downloading a file. This, however can still propose a problem when someone is the function to download a tokenized file where the path can be long.

In the case where the headers of the response provide a content-disposition header including a file name, it would be ideal to have the download_url function respect this file name and move the file name (which by default is the token in the path) to the file name requested.

[johnjamesjacoby]

Let's try to make this happen 5.8.