Use of importNode and complete document in filter adds many meta elements to output

Here's a failing test

Here's the fix
I also did some cleanup of how you're collecting cacheable metadata in case any of the plugins do something like check access or render an entity and therefore emit cache info like contexts, tags, max-age.

Much cleaner and with the test and all. thank you very much. Will have a look at this over the next couple of days.

Visual review, looks good to me.

@Nuez dont forget to add test runners at https://www.drupal.org/node/3306172/qa → . Once they're added we should be able to do manual runs from this issue.

Automatically closed - issue fixed for 2 weeks with no activity.