💥 Remove :feature category

:feature was a "catch-all" category. Many of its modules fit better in
other categories, so they've been moved:

- feature/debugger -> tools/debugger
- feature/evil -> editor/evil
- feature/eval -> tools/eval
- feature/lookup -> tools/lookup
- feature/snippets -> editor/snippets
- feature/file-templates -> editor/file-templates
- feature/workspaces -> ui/workspaces

More potential changes in the future:

- A new :term category for terminal emulation modules (eshell, term and
  vterm).
- A new :os category for modules dedicated to os-specific functionality.
  The :tools macos module would fit here, but so would modules for nixos
  and arch.
- A new :services category for web-service integration, like wakatime,
  twitter, elfeed, gist and pastebin services.

modules/completion/helm/autoload/helm.el

@@ -24,8 +24,8 @@
   "A version of `helm-buffers-list' with its buffer list restricted to the
 current workspace."
   (interactive)
-  (unless (featurep! :feature workspaces)
-    (user-error "This command requires the :feature workspaces module"))
+  (unless (featurep! :ui workspaces)
+    (user-error "This command requires the :ui workspaces module"))
   (with-no-warnings
     (with-persp-buffer-list nil (helm-buffers-list))))
 
@@ -34,8 +34,8 @@ current workspace."
   "A version of `helm-mini' with its buffer list restricted to the current
 workspace."
   (interactive)
-  (unless (featurep! :feature workspaces)
-    (user-error "This command requires the :feature workspaces module"))
+  (unless (featurep! :ui workspaces)
+    (user-error "This command requires the :ui workspaces module"))
   (with-no-warnings
     (with-persp-buffer-list nil (helm-mini))))