Editora 0.18.3. Archived, so links from that release keep working. Read the 0.18.5 page →
Buffer: Copy Path
buffer.copyPath Copy the current file's full path to the clipboard.
How to run it
Open the command palette (M-x in the Emacs keymap) and search for Buffer: Copy Path, then press Enter. It has no default keybinding, but you can bind one in Settings → Keymaps.