Manage in Customizer lacks return param for Widgets admin page

[westonruter]

In #28032 we introduced a “Manage in Customizer” link on the Widgets admin page. This link opens the Customizer and auto-opens the Widgets panel (#28650). In #25457 we added return URL param for Customizer links in the WP Admin so that when the user clicks “Close” in the Customizer they are returned to the URL that they were on before being navigated to the Customizer. This was not done for the “Manage in Customizer” link on the Widgets admin page. When clicking this link and then clicking “Close” in the Customizer, the user should be taken back to the Widgets admin page as opposed to the Themes admin page.

[celloexpressions]

Actually, I thought that was intentional. The point of that link is to get them to start using the Customizer instead of the admin page, so why should we take them back to the admin page when they're done?

Thinking more broadly, I'm starting to think that the front page on the front end might be a more appropriate default return location that themes in the admin, although I don't think we're quite ready for that yet.

[westonruter]

The widgets admin page is the only place where you can fully delete widgets (remove them from the inactive widgets sidebar). Also, I don't think the widgets admin page is going anywhere. I believe the decision to go with a “Manage in Customizer” link at the top instead of going with an nag notice was because of this as well, that we're not trying to direct users away from the widgets admin page (not yet, anyway).

[tywayne]

After reading through the discussion on #25457 I don't see Widgets being an exception to the return after closing approach. Patch added in case that is the consensus.

[DrewAPicture]

Patch still applies and works as expected, though I would question why we're pointing the user back to the REQUEST_URI instead of explicitly pointing them to widgets.php.

[tywayne]

REQUEST_URI was used to ensure a return to whatever view of widgets.php they actually came from.

For example, let's say a theme or plugin provided a filtered view of widgets.php, showing only widget areas for specific layouts/templates using a query string (iThemes Builder does exactly that.)

If we explicitly point them to widgets.php, they'd lose the filtered view they came from.

[ocean90]

In 31420:

Widgets: Add return param for widgets admin page to the "Manage in Customizer" link.

props tywayne.
fixes #30888.