Editor: throttle scrolling of the main window when the editor is active and is...

Editor: throttle scrolling of the main window when the editor is active and is being scrolled with the mouse wheel or a trackpad, see #27013
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git-svn-id: https://core.svn.wordpress.org/trunk@27218 1a063a9b-81f0-0310-95a4-ce76da25c4cd