Revisions for code edits

[karmatosed]

We should let people restore previous versions of their code in case they make mistakes.

More details TBA.

[ocean90]

Some links for that:

• ​https://nacin.com/2010/03/17/google-summer-of-code-idea/
• ​https://wordpress.org/plugins/code-revisions/
• ​https://make.wordpress.org/core/tag/code-revisions/
• ​https://wptavern.com/should-code-revisions-be-added-to-the-wordpress-core

[adamsilverstein]

I can confirm that the ​code-revisions plugin still works as expected despite not being updated. If we want to merge something like this to core, I am happy to work on a patch.