Add wp.hooks - JavaScript actions and filters.
Add a JavaScript hooks library with an API that mirrors the WordPress Plugin API; provides similar functionality and API to PHP hooks.
Called via the global `wp.hooks`, eg: `wp.hooks.addAction()`, etc. Adds:
* `addAction( 'hook', 'vendor/plugin/function', callback, priority )`
* `addFilter( 'hook', 'vendor/plugin/function', callback, priority )`
* `removeAction( 'hook', 'vendor/plugin/function' )`
* `removeFilter( 'hook', 'vendor/plugin/function' )`
* `removeAllActions( 'hook' )`
* `removeAllFilters( 'hook' )`
* `doAction( 'hook', arg1, arg2, moreArgs, finalArg )`
* `applyFilters( 'hook', content, arg1, arg2, moreArgs, finalArg )`
* `doingAction( 'hook' )`
* `doingFilter( 'hook' )`
* `didAction( 'hook' )`
* `didFilter( 'hook' )`
* `hasAction( 'hook' )`
* `hasFilter( 'hook' )`
Props adamsilverstein, jnylen0, aduth, kadamwhite, youknowriad, schlessera, mikeschinkel, azaozz, vhauri, CaptainN, scribu, carldanley, chetanchauhan, mgibbs189, stephenharris, justnorris, koopersmith, gcorne, TV productions, atimmer.
Fixes #21170.
git-svn-id: https://develop.svn.wordpress.org/trunk@41375 602fd350-edb4-49c9-b593-d223f7449a82
1b7475645a