Create a new Backbone view, `media.view.Label`, which can be used as a subview in things like toolbars, which need screen reader text.

Make an initial instance of it for the label for Bulk Actions in Media Grid.

See #29026.

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Media Grid: add screen reader text in a subview on the toolbar, a `media.view.Label` instance before `media.view.DateFilter`.

See #29026.

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Revert styling changes to the Attachment Details modal from [29289]. fixes #28844.

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Media Grid: use a `media.view.Label` instance in the toolbar for the screen reader text for Search.

See #29026.

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Media Grid: 

* Use a `media.view.Label` instance in the toolbar for the screen reader text for the "all" dropdown.
* Adjust the spinner's priority.

Fixes #29026.

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JSHint after [29437].


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Mark `WP_List_Table::bulk_actions()`'s argument `$which` as optional for BC.

Fixes #29026.

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After [29360], add rules for `<input>`s in the scope of `.media-sidebar`.

Props ocean90.
Fixes #28647.

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`wp_dashboard_cached_rss_widget()` contained some `func_get_args()` code that was indescribably weird.
This keeps it weird, but makes sure that `$check_urls` gets passed to the callback.

Props michalzuber, ocean90.
Fixes #28872.

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Media Grid: remove Router code that doesn't actually ever run.

See #29121.

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Media Grid: remove Router code that doesn't actually ever run.

See #29121.

Built from https://develop.svn.wordpress.org/trunk@29444


git-svn-id: http://core.svn.wordpress.org/trunk@29222 1a063a9b-81f0-0310-95a4-ce76da25c4cd
4.0-beta3-29445

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