Git: Annotate Previous Revision
git.blamePreviousRevision Open the file as it was before the commit the caret line is blamed on, annotated in turn.
How to run it
Open the command palette (M-x in the Emacs keymap) and search for Git: Annotate Previous Revision, then press Enter. It has no default keybinding, but you can bind one in Settings → Keymaps.