Editor-expand: reset the editor height after the window is resized.

Merges [29886] to the 4.0 branch.

props azaozz.
fixes #29952.

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git-svn-id: http://core.svn.wordpress.org/branches/4.0@30251 1a063a9b-81f0-0310-95a4-ce76da25c4cd