PluginNotFoundException when plugin is renamed

Problem/Motivation

If an in-use plugin is renamed or removed, visiting any page that uses that plugin will result in PluginNotFoundException: The "PLUGIN_ID" plugin does not exist.

Steps to reproduce

Use a plugin on a page manager page, such as by adding an access plugin to a page. Change the plugin's ID. Visit the page or try to edit access on that page.

Proposed resolution

This exception should be caught. For a page, a missing access plugin should result in a 403 status. For the edit access page, admin/structure/page_manager/manage/PAGE_ID/access, the page should appear with the plugin labelled as being missing, allowing the user to delete the condition.