TYPO3 Core

Is it possible to make backend panels resizable again, like in 7.x and below? I mean left module menu and pagetree. And I'm not talking about collapse button, but specifically about mouse resize, like it used to work since always. Is there any option or extension to restore this functionality in any way? Or to configure pagetree panel width in user or global config? It really makes me angry now.
Or someone could point me to classes in core, which I could xclass to make an external extension with this functionality.