Refactor instance security dashboard permissions

* Refactor metaprogramming in SecurityDashboardPermissions to avoid
    needing to overwrite InstanceSecurityDashboard.name
* Rename InstancePolicy to InstanceSecurityDashboardPolicy

https://gitlab.com/gitlab-org/gitlab/issues/202521

ee/app/controllers/concerns/security_dashboards_permissions.rb

@@ -3,6 +3,12 @@
 module SecurityDashboardsPermissions
   extend ActiveSupport::Concern
 
+  VULNERABLE_POLICIES = {
+    group: :read_group_security_dashboard,
+    instance_security_dashboard: :read_instance_security_dashboard,
+    project: :read_project_security_dashboard
+  }.freeze
+
   included do
     before_action :ensure_security_dashboard_feature_enabled!
     before_action :authorize_read_security_dashboard!
@@ -19,6 +25,6 @@ module SecurityDashboardsPermissions
   end
 
   def read_security_dashboard
-    "read_#{vulnerable.class.name.underscore}_security_dashboard".to_sym
+    VULNERABLE_POLICIES[vulnerable.class.name.underscore.to_sym]
   end
 end

ee/app/models/instance_security_dashboard.rb

@@ -3,10 +3,6 @@
 class InstanceSecurityDashboard
   extend ActiveModel::Naming
 
-  def self.name
-    'Instance'
-  end
-
   def initialize(user, project_ids: [])
     @project_ids = project_ids
     @user = user

ee/app/policies/instance_policy.rb → ee/app/policies/instance_security_dashboard_policy.rb

 # frozen_string_literal: true
 
-class InstancePolicy < BasePolicy
+class InstanceSecurityDashboardPolicy < BasePolicy
   rule { ~anonymous }.enable :read_instance_security_dashboard
 end

ee/spec/models/instance_security_dashboard_spec.rb

@@ -17,12 +17,6 @@ describe InstanceSecurityDashboard do
 
   subject { described_class.new(user, project_ids: project_ids) }
 
-  describe '.name' do
-    it 'is programmatically named Instance' do
-      expect(described_class.name).to eq('Instance')
-    end
-  end
-
   describe '#all_pipelines' do
     it 'returns pipelines for the projects with security reports' do
       expect(subject.all_pipelines).to contain_exactly(pipeline1)

ee/spec/policies/instance_policy_spec.rb → ee/spec/policies/instance_security_dashboard_policy_spec.rb

@@ -2,7 +2,7 @@
 
 require 'spec_helper'
 
-describe InstancePolicy do
+describe InstanceSecurityDashboardPolicy do
   let(:current_user) { create(:user) }
   let(:user) { create(:user) }