This aims to reduce ambiguity about what exactly is the "first" or "last" revision, and bring more consistency with similar wording elsewhere in core, e.g. latest posts, latest comments, etc.
This affects:
* `wp_save_post_revision()`
* `wp_prepare_revisions_for_js()`
* `WP_Customize_Manager::filter_revision_post_has_changed()`
Follow-up to [53759], [53769], [53778].
Props peterwilsoncc.
Fixes#55857.
Built from https://develop.svn.wordpress.org/trunk@53779
git-svn-id: http://core.svn.wordpress.org/trunk@53338 1a063a9b-81f0-0310-95a4-ce76da25c4cd