🐞 Bug Report: Every FAIR-enabled plugin or theme results in a new `Updater` instance adding its hooks

[johnbillion]

A new instance of the Updater class gets instantiated for every FAIR-enabled plugin or theme in place on a site. This causes all of the hooks in the load_hooks() method to be added and executed once per plugin and theme, instead of once globally.

Detailed Description

This causes hooks such as upgrader_source_selection, plugins_api, site_transient_update_plugins, wp_prepare_themes_for_js, and upgrader_pre_download to be run n times instead of once.

This causes a few effects, including:

• Updater::upgrader_source_selection() attempts to rename and move every plugin and theme n times instead of once.
• verify_signature_on_download() downloads and verifies every package n times instead of once. As far as I can tell, there is no poisoning of the trusted key logic between plugins but I think this is by luck rather than by design.
• Updater::repo_api_details() runs n times instead of once, although this does contain a guard condition so it doesn't re-fetch package data n times, although it does parse and recalculate the DID hash n times instead of once.
• Updater::customize_theme_update_html() runs n times instead of once, which calls Updater::append_theme_actions_content() n times instead of once. I don't have any FAIR-enabled themes installed, but if I had more than one I anticipate that this would cause duplicate update messages to appear for a theme with a pending update.

The other effect this has is that I am unable to propose some enhancements that I want to make to verify_signature_on_download() because it unexpectedly runs with the incorrect DID context n-1 times out of n.

Expected Behavior

The hooks that the Updater class hooks into and handles should only be instantiated once. I think this means that the Updater class needs to be rearchitected so it acts as a registry and dispatches any plugin- or theme-specific logic as necessary.

[johnbillion]

Here is a plugin that adds a FAIR panel to Query Monitor to show the duplicate concerned filters: fair-qm.php. To use it, install it and then visit Query Monitor -> FAIR -> Hooks in Use.