Upgrade/Install: Add `hook_extra` parameter to the `upgrader_pre_download` filter.

This provides additional context to code running on this hook, including which plugin or theme update will be downloaded. It also brings consistency to this filter with others throughout the upgrade process.

Props obliviousharmony, desrosj.
Fixes #49686.
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git-svn-id: https://core.svn.wordpress.org/trunk@48168 1a063a9b-81f0-0310-95a4-ce76da25c4cd