Editora 0.20.0. Archived, so links from that release keep working. Read the 0.24.0 page →
View: Split Tool Window Side
view.splitToolWindow Open a tool window beside the one already on its side.
How to run it
Open the command palette (M-x in the Emacs keymap) and search for View: Split Tool Window Side, then press Enter. It has no default keybinding, but you can bind one in Settings → Keymaps.