[ios] Pass NSURLResponse information to DownloadNativeTaskImpl

Ensure that HTTP response code and the response MIME type information
is propagated from WKDownload to DownloadNativeTaskImpl.

Bug: none
Change-Id: I0af8abc7b5b0cb693ad5f53535fb511fbc08dbc3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3627576


Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Ali Juma <ajuma@chromium.org>
Cr-Commit-Position: refs/heads/main@{#999804}