DEV: Replace custom Onebox symbolize_keys implementation with ActiveSupport (#23828)

We have a custom implementation of #symbolize_keys in our Onebox helpers. This is likely a legacy from when Onebox was a standalone gem. This change replaces all usages with either #deep_symbolize_keys from ActiveSupport, or appropriate option to the JSON parser gem used.

lib/onebox/oembed.rb

@@ -3,7 +3,7 @@
 module Onebox
   class Oembed < OpenGraph
     def initialize(response)
-      @data = Onebox::Helpers.symbolize_keys(::MultiJson.load(response))
+      @data = ::MultiJson.load(response, symbolize_keys: true)
 
       # never use oembed from WordPress 4.4 (it's broken)
       @data.delete(:html) if @data[:html] && @data[:html]["wp-embedded-content"]