Add experimental Trash module

Would it be possible to document why the decision was made to postpone this on the Workspaces? This module doesn't directly depend on Workspaces so it isn't self-explanatory why we would make it a hard blocker for this issue.

@lauriii we shouldn't add a new experimental module that is dealing with deep entity system architecture while we have one already in core that's not stable yet. And more specifically, the time spent working on trash module instead of resolving fundamental blockers to workspaces being is part of the reasons it didn't reach stable 2-3 years ago.

No longer postponed on Workspaces

Note there's now a stable trash module in contrib https://www.drupal.org/project/trash →

I haven't personally used it, but I believe it is the result of @amateescu's comment in #50.