Problem/Motivation
Split from #3257725: Add a cache prewarm API because #3056604: Add/remove event listeners provided by a module on module install/uninstall means there can be side-effects to rebuilding caches in the same request that a module has been uninstalled.
Places that could use post-response cache prewarming:
1. The end of the installer - so the first request to the site is snappy.
2. After running updates in the UI.
3. After pressing the 'clear caches' button in the UI
4. After installing a module or theme in the UI.
5. After uninstalling a module or theme in the UI.
