Enable Performance/ChainArrayAllocation cop

But only for the `import_export` module for now, where we know
this has been a problem before.

Also fixed the 3 problems it found.

.rubocop.yml

@@ -380,6 +380,13 @@ Cop/BanCatchThrow:
 Performance/ReadlinesEach:
   Enabled: true
 
+Performance/ChainArrayAllocation:
+  Enabled: true
+  Include:
+    - 'lib/gitlab/import_export/**/*'
+    - 'ee/lib/gitlab/import_export/**/*'
+    - 'ee/lib/ee/gitlab/import_export/**/*'
+
 # https://gitlab.com/gitlab-org/gitlab/-/issues/212541
 RSpec/RepeatedExample:
   Exclude:

lib/gitlab/import_export/attributes_finder.rb

@@ -38,7 +38,7 @@ module Gitlab
       def resolve_preloads(model_key, model_tree)
         model_tree
           .map { |submodel_key, submodel_tree| resolve_preload(model_key, submodel_key, submodel_tree) }
-          .compact
+          .tap { |entries| entries.compact! }
           .to_h
           .deep_merge(@preloads[model_key].to_h)
           .presence

lib/gitlab/import_export/fast_hash_serializer.rb

@@ -100,7 +100,7 @@ module Gitlab
 
         includes
           .map(&method(:serialize_include_definition))
-          .compact
+          .tap { |entries| entries.compact! }
           .to_h
       end
 

lib/gitlab/import_export/relation_tree_restorer.rb

@@ -142,9 +142,9 @@ module Gitlab
       end
 
       def build_relations(relation_key, relation_definition, data_hashes)
-        data_hashes.map do |data_hash|
-          build_relation(relation_key, relation_definition, data_hash)
-        end.compact
+        data_hashes
+          .map { |data_hash| build_relation(relation_key, relation_definition, data_hash) }
+          .tap { |entries| entries.compact! }
       end
 
       def build_relation(relation_key, relation_definition, data_hash)