Docs: Move the canonical DocBlock for `handle_bulk_actions-{$screen}` action...

Docs: Move the canonical DocBlock for `handle_bulk_actions-{$screen}` action to `wp-admin/edit.php`.

* Document accepted values for the `$items` parameter.
* Use interpolated syntax for the filter name.

Props dilipbheda, johnbillion, SergeyBiryukov.
Fixes #48857.
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git-svn-id: https://core.svn.wordpress.org/trunk@46611 1a063a9b-81f0-0310-95a4-ce76da25c4cd