Cleaner implementation of visible_to_user?

This splits the ability check into two parts: the capability name and
the object of the check, simplifying matters considerably and reducing
repetition.

app/models/event.rb

@@ -135,29 +135,11 @@ class Event < ApplicationRecord
     super(presenter_class: ::EventPresenter)
   end
 
-  # rubocop:disable Metrics/CyclomaticComplexity
-  # rubocop:disable Metrics/PerceivedComplexity
   def visible_to_user?(user = nil)
-    if push_action? || commit_note?
-      Ability.allowed?(user, :download_code, project)
-    elsif membership_changed?
-      Ability.allowed?(user, :read_project, project)
-    elsif created_project_action?
-      Ability.allowed?(user, :read_project, project)
-    elsif issue? || issue_note?
-      Ability.allowed?(user, :read_issue, note? ? note_target : target)
-    elsif merge_request? || merge_request_note?
-      Ability.allowed?(user, :read_merge_request, note? ? note_target : target)
-    elsif personal_snippet_note? || project_snippet_note?
-      Ability.allowed?(user, :read_snippet, note_target)
-    elsif milestone?
-      Ability.allowed?(user, :read_milestone, project)
-    else
-      false # No other event types are visible
-    end
+    return false unless capability.present?
+
+    Ability.allowed?(user, capability, permission_object)
   end
-  # rubocop:enable Metrics/PerceivedComplexity
-  # rubocop:enable Metrics/CyclomaticComplexity
 
   def resource_parent
     project || group
@@ -364,8 +346,38 @@ class Event < ApplicationRecord
     Event._to_partial_path
   end
 
+  protected
+
+  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
+                      end
+                    end
+  end
+
   private
 
+  def permission_object
+    if note?
+      note_target
+    elsif target_id.present?
+      target
+    else
+      project
+    end
+  end
+
   def push_action_name
     if new_ref?
       "pushed new"

ee/app/models/ee/event.rb

@@ -18,15 +18,21 @@ module EE
       scope :epics, -> { where(target_type: 'Epic') }
     end
 
-    override :visible_to_user?
-    def visible_to_user?(user = nil)
-      if epic?
-        Ability.allowed?(user, :read_epic, target)
-      elsif epic_note?
-        Ability.allowed?(user, :read_epic, note_target)
-      else
-        super
-      end
+    override :capability
+    def capability
+      @capability ||= begin
+                        if epic? || epic_note?
+                          :read_epic
+                        elsif design_note?
+                          :read_design
+                        else
+                          super
+                        end
+                      end
+    end
+
+    def design_note?
+      note? && note.for_design?
     end
 
     def epic_note?