Add stable checksum to the JSON API

Library/Homebrew/formula.rb

@@ -2107,6 +2107,7 @@ class Formula
         "url"      => stable.url,
         "tag"      => stable.specs[:tag],
         "revision" => stable.specs[:revision],
+        "checksum" => stable.checksum&.to_s,
       }
 
       hsh["bottle"]["stable"] = bottle_hash if bottle_defined?

Library/Homebrew/formulary.rb

@@ -159,6 +159,7 @@ module Formulary
         stable do
           url urls_stable["url"]
           version json_formula["versions"]["stable"]
+          sha256 urls_stable["checksum"] if urls_stable["checksum"].present?
         end
       end