Reduce perceived complexity of capability computation

This changes the capability computation from code (a very large if
statement) to transformation of static data.

The data we transform is a map from `ability` to `requirements`:

```ruby
{
  ability_needed: [:test_one?, :test_two?],
  other_ability: [:test_three?]
}
```

If the object passes _any_ of the requirement tests, then it must pass
the policy ability check for all of the matched abilities. If the tests
are inductive then this becomes a one-to-one reverse mapping, but it
need not be, so this formulation can actually express stricter policy
tests than the current if statement can (i.e. we can assert that some
event needs multiple abilities).

This change expresses (like a DSL) the rules as symbols that must be
implemented as methods on the receiver, so we need to `send` the
requirements to the receiving event.

app/models/event.rb

@@ -149,7 +149,9 @@ class Event < ApplicationRecord
   def visible_to_user?(user = nil)
     return false unless capability.present?
 
-    Ability.allowed?(user, capability, permission_object)
+    capability.all? do |rule|
+      Ability.allowed?(user, rule, permission_object)
+    end
   end
 
   def resource_parent
@@ -361,34 +363,30 @@ class Event < ApplicationRecord
 
   protected
 
-  # rubocop:disable Metrics/CyclomaticComplexity
-  # rubocop:disable Metrics/PerceivedComplexity
-  #
-  # TODO Refactor this method so we no longer need to disable the above cops
-  # https://gitlab.com/gitlab-org/gitlab/-/issues/216879.
   def capability
     @capability ||= begin
-                      if push_action? || commit_note?
-                        :download_code
-                      elsif membership_changed? || created_project_action?
-                        :read_project
-                      elsif issue? || issue_note?
-                        :read_issue
-                      elsif merge_request? || merge_request_note?
-                        :read_merge_request
-                      elsif personal_snippet_note? || project_snippet_note?
-                        :read_snippet
-                      elsif milestone?
-                        :read_milestone
-                      elsif wiki_page?
-                        :read_wiki
-                      elsif design_note? || design?
-                        :read_design
-                      end
-                    end
-  end
-  # rubocop:enable Metrics/CyclomaticComplexity
-  # rubocop:enable Metrics/PerceivedComplexity
+      capabilities.flat_map do |ability, syms|
+        if syms.any? { |sym| send(sym) } # rubocop: disable GitlabSecurity/PublicSend
+          [ability]
+        else
+          []
+        end
+      end
+    end
+  end
+
+  def capabilities
+    {
+      download_code: %i[push_action? commit_note?],
+      read_project: %i[membership_changed? created_project_action?],
+      read_issue: %i[issue? issue_note?],
+      read_merge_request: %i[merge_request? merge_request_note?],
+      read_snippet: %i[personal_snippet_note? project_snippet_note?],
+      read_milestone: %i[milestone?],
+      read_wiki: %i[wiki_page?],
+      read_design: %i[design_note? design?]
+    }
+  end
 
   private
 

ee/app/models/ee/event.rb

@@ -15,15 +15,9 @@ module EE
       scope :epics, -> { where(target_type: 'Epic') }
     end
 
-    override :capability
-    def capability
-      @capability ||= begin
-                        if epic? || epic_note?
-                          :read_epic
-                        else
-                          super
-                        end
-                      end
+    override :capabilities
+    def capabilities
+      super.merge(read_epic: %i[epic? epic_note?])
     end
 
     override :action_name