when Matomo for WP is symlinked into WP, Twig src rewriting for non-core plugins creates incorrect URLs

[diosmosis]

To reproduce:

• symlink Matomo for WordPress into wp-content/plugins/matomo (or just use the local dev environment)
• install a plugin like CrashAnalytics and track something
• view the Visits Log, custom action <img>s for the plugin installed (like crash.png) will have the wrong src=

The problem occurs in core in Theme.php. The only solution is switching to using WordPress' plugins_url() function, but since there is no way to hook into Theme currently, this is nontrivial to add.