Editora 0.9.10. Archived, so links from that release keep working. Read the 0.18.5 page →
Edit: Swap Case
edit.case.swap Invert the case of every letter in the selection or the identifier at the caret.
How to run it
Open the command palette (M-x in the Emacs keymap) and search for Edit: Swap Case, then press Enter. It has no default keybinding, but you can bind one in Settings → Keymaps.