Media Upload: Improve styling of error messages.

props afercia, michalzuber.
fixes #29047.
Built from https://develop.svn.wordpress.org/trunk@29355


git-svn-id: http://core.svn.wordpress.org/trunk@29131 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Attach Media: Display the correct error message when search result is empty.

fixes #29093.
Built from https://develop.svn.wordpress.org/trunk@29356


git-svn-id: http://core.svn.wordpress.org/trunk@29132 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Upgrader: Use always `window.postMessage` for decrement of update count bubbles when `IFRAME_REQUEST` is defined.
Fixes decrement of translation update count bubbles when updated through the bulk upgrader.

fixes #29054.
Built from https://develop.svn.wordpress.org/trunk@29357


git-svn-id: http://core.svn.wordpress.org/trunk@29133 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Language Upgrader: Don't print a footer when translations are updated async.

fixes #28947.
Built from https://develop.svn.wordpress.org/trunk@29358


git-svn-id: http://core.svn.wordpress.org/trunk@29134 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Plugin install: Improve styling of the no results message.

see #28753.
Built from https://develop.svn.wordpress.org/trunk@29359


git-svn-id: http://core.svn.wordpress.org/trunk@29135 1a063a9b-81f0-0310-95a4-ce76da25c4cd