Replace `class_eval` with `define_method` for enum

https://github.com/rails/rails/commit/db41eb8a6ea88b854bf5cd11070ea4245e1639c5#commitcomment-4502683
Fix changelog indent [ci skip]
Fix typo in railties changelog

Also improve the example to show as shell command [ci skip]
Merge pull request #12754 from ck3g/replace-class-evals-with-define-method-for-enum

Replace `class_eval` with `define_method` for enum
:scissors: [ci skip]
Remove extra whitespace

When generating an app with --skip_active_record, an extra
line of whitespace was included unnecessarily.
Respect cache timestamp format when giving timestamps to #cache_key
Refactor logic to grab the max time of the list of timestamp names in #cache_key

Reuse the already existing logic used for grabbing this information from
the updated columns.
Merge pull request #12755 from cbartlett/master

Remove extra whitespace
Style fixes on test schema file
Convert schema file to ruby 1.9 style hash
Fix failures related to enum changes

Commit 6e4a810f51b9ed2468b92247ef5568cc9d6dbcc0 changed the implementation
from class_eval to define_method, but missed the access to the constant
versus the access to the constant name.
document `BACKTRACE` env var usage in testing guide. [ci skip]