(Sources-2) oak_db::workspace_dependencies()

[DavisVaughan]

Progress towards #1234
Branched from #1286

Two new things here:

• File::used_packages() is a tracked query that returns the Names of all packages used by this file

  • library() and require() are included (reusing the existing attached_packages())
  • :: and ::: are included (using the new namespaced_accesses() from (Sources-1) Teach SemanticIndex about NamespacedAccesses #1286)
  • The result is sorted and unique, maximizing the chance of backdating after small file edits (a reorder of library() or :: calls should not affect this query result, unlike attached_packages())

• oak_db::workspace_dependencies() is a tracked query that returns a Vec<Package> of every installed package used by this workspace.

  • It collects from File::used_packages() on each workspace_file()
  • It collects from DESCRIPTION if you have a workspace package open. In particular, it collects Imports and Depends. I have omitted Suggests because typically they are referenced by :: already if they are used, so they probably aren't worth it to also include here?

Two notes about oak_db::workspace_dependencies():

• Any not installed package returned by File::used_packages() is thrown out. The user can't actually use this, and we won't have a package version to look up anyways.
• If you have a workspace package open, it is also removed from the list (the workspace package itself isn't really a workspace dependency). We assume that you already have package sources for that in your local R/ folder.

oak_db::workspace_dependencies() will be used in a future PR to detect the set of changed packages after each revision change.