Currently themes can declare support for a given feature by using add_theme_support(). This commit adds a register_theme_feature() API that allows plugins and WordPress Core to declare a list of available features that themes can support.
The REST API uses this to expose a theme's supported features if the feature has been registered with "show_in_rest" set to true.
Props kadamwhite, spacedmonkey, williampatton, desrosj, TimothyBlynJacobs.
Fixes#49406.
git-svn-id: https://develop.svn.wordpress.org/trunk@48171 602fd350-edb4-49c9-b593-d223f7449a82
9a604011ee