Media: when copying from "caption" (textarea) to "alt" (text input) also...

Media: when copying from "caption" (textarea) to "alt" (text input) also remove line breaks, props kovshenin, fixes #23176 for trunk

git-svn-id: https://core.svn.wordpress.org/trunk@23298 1a063a9b-81f0-0310-95a4-ce76da25c4cd