FIX: participating users statistics... (#29293)

* FIX: participating users statistics...

... was (mis-)counting

- bots
- anonymous users
- suspended users

There's now a "valid_users" function that holds the AR query for valid users and which is used in all "users", "active_users", and "participating_users" queries.

Internal ref - t/138435

app/models/user.rb

@@ -303,6 +303,7 @@ class User < ActiveRecord::Base
   scope :not_suspended, -> { where("suspended_till IS NULL OR suspended_till <= ?", Time.zone.now) }
   scope :activated, -> { where(active: true) }
   scope :not_staged, -> { where(staged: false) }
+  scope :approved, -> { where(approved: true) }
 
   scope :filter_by_username,
         ->(filter) do