Upgrade/Install: Pass the plugin file path into the plugin_auto_update_debug_string filter.

Adds better tooling for when user specific plugins can be updated, but platform specific ones cannot.

This brings [48696] to the 5.5 branch.

Fixes #50821.

Props bpayton, pbiron, audrasjb, SergeyBiryukov, whyisjake.

Built from https://develop.svn.wordpress.org/branches/5.5@48697


git-svn-id: https://core.svn.wordpress.org/branches/5.5@48459 1a063a9b-81f0-0310-95a4-ce76da25c4cd