Laziness improvements

This makes our lazy aggregates support a common interface, and adds
aync-catch to `Lazy`.

ee/lib/gitlab/graphql/aggregations/epics/lazy_epic_aggregate.rb

@@ -6,6 +6,7 @@ module Gitlab
       module Epics
         class LazyEpicAggregate
           include ::Gitlab::Graphql::Aggregations::Epics::Constants
+          include ::Gitlab::Graphql::Deferred
 
           attr_reader :facet, :epic_id, :lazy_state
 
@@ -49,6 +50,8 @@ module Gitlab
             @block ? @block.call(node, object) : object
           end
 
+          alias_method :execute, :epic_aggregate
+
           private
 
           def validate_facet(aggregate_facet)

ee/lib/gitlab/graphql/aggregations/issues/lazy_block_aggregate.rb

@@ -5,6 +5,8 @@ module Gitlab
     module Aggregations
       module Issues
         class LazyBlockAggregate
+          include ::Gitlab::Graphql::Deferred
+
           attr_reader :issue_id, :lazy_state
 
           def initialize(query_ctx, issue_id, &block)
@@ -35,6 +37,8 @@ module Gitlab
             result
           end
 
+          alias_method :execute, :block_aggregate
+
           private
 
           def load_records_into_loaded_objects

ee/lib/gitlab/graphql/aggregations/vulnerabilities/lazy_user_notes_count_aggregate.rb

@@ -5,6 +5,8 @@ module Gitlab
     module Aggregations
       module Vulnerabilities
         class LazyUserNotesCountAggregate
+          include ::Gitlab::Graphql::Deferred
+
           attr_reader :vulnerability, :lazy_state
 
           def initialize(query_ctx, vulnerability)

lib/gitlab/graphql/lazy.rb

@@ -17,6 +17,14 @@ module Gitlab
         self.class.new { yield force }
       end
 
+      def catch(error_class = StandardError, &block)
+        self.class.new do
+          force
+        rescue error_class => e
+          yield e
+        end
+      end
+
       # Force evaluation of a (possibly) lazy value
       def self.force(value)
         case value