[#3484] Add missing argument to Hash default proc (#3486)

The proc to fill in a default value for a Hash accepts
two arguments: the hash itself and then the key.  Prior
to this commit, our proc was only using the Hash, but
was treating it as if it was a key.  This had the potential
to cause some serious performance problems when solr
returned many facets or many facet values, when a huge
hash was treated as a string and interpolated into other
strings via Hash#inspect.

Adding this missing argument ensures that we send the
key/field_name, rather than the entire hash.  For the
provided test case on my laptop, this commit speed up
null facet object generation up from 45 iterations/second
to 18,700 iterations/second.  It also doubles the
performance of our advanced search form.

This commit also adds the rspec-benchmark gem as a
dev dependency -- I'm definitely open to figuring out
a different way to test this if the additional dependency
is not desired.

Closes #3484

Co-authored-by: Christina Chortaria <christinach@users.noreply.github.com>
Co-authored-by: Kevin Reiss <kevinreiss@users.noreply.github.com>
Co-authored-by: Max Kadel <maxkadel@users.noreply.github.com>

blacklight.gemspec

@@ -49,6 +49,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency "rubocop-capybara"
   s.add_development_dependency "rubocop-rspec_rails"
   s.add_development_dependency "rubocop-factory_bot"
+  s.add_development_dependency "rspec-benchmark"
   s.add_development_dependency "i18n-tasks", '~> 1.0'
   s.add_development_dependency "solr_wrapper"
 end

lib/blacklight/solr/response/facets.rb

@@ -157,7 +157,7 @@ def merge_facet(name:, value:, hits: nil)
   #   facet data in the response
   def default_aggregations
     @default_aggregations ||= begin
-      h = Hash.new { |key| null_facet_field_object(key) }
+      h = Hash.new { |_hash, key| null_facet_field_object(key) }
       h.with_indifferent_access
     end
   end