Restore Configurable Actions to core

Restore Configurable Actions to core

Configurable actions became unusable when Trigger module was removed from core. They were removed shortly thereafter. Configurable actions became realistic again when Views Bulk Operations went into core, but were never restored.

I would like to propose that we add back the 6 Configurable actions that were removed from core, but instead of that code living in a separate module (trigger) it become part of Views Bulk Operations.

The actions to restore are as follows: * Display a message to the user * Send e-mail * Redirect to URL * Change the author of content * Unpublish content containing keyword(s) * Unpublish comment containing keyword(s)

A good contrib module to test the APIs for configurable actions would be Flag.

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Original Issue:

Change introduced in https://github.com/backdrop/backdrop-issues/issues/168

Nothing in https://api.backdropcms.org/api/backdrop/core%21modules%21system%21syste... tells that configurable actions are no more available.