Use more generic, reusable CSS for the filter bar on Add Themes. This will allow us to reuse the UI in other places, such as the Media Library. props paulwilde. fixes #28794.

Built from https://develop.svn.wordpress.org/trunk@29217


git-svn-id: http://core.svn.wordpress.org/trunk@29001 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Install Plugins screen:

* Utilize the (currently-named) filter bar from the Add Themes screen.
* Move the upload link to the h2, also like the Add Themes screen.

see #28673.

Built from https://develop.svn.wordpress.org/trunk@29218


git-svn-id: http://core.svn.wordpress.org/trunk@29002 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Plugin install cards:

* Move author attribution to its own line.
* Use `esc_url()` where appropriate.
* Better i18n.
* min-height for cards for a more even appearance.
* Show more cards on wide screens.
* Tighten up spacing below the filter bar.

props ocean90, helen. see #28785.

Built from https://develop.svn.wordpress.org/trunk@29219


git-svn-id: http://core.svn.wordpress.org/trunk@29003 1a063a9b-81f0-0310-95a4-ce76da25c4cd