message: Fix `<BS>` in leading whitespace with tabs
  It's still a bit janky with mixed indentation, but that's not a priority for now.
  Fixes
diff: @@ -241,7 +241,7 @@ class CommandBackspaceInInsertMode extends BaseCommand {
  } else if (
  position.character > 0 &&
  position.character <= leadingSpaces &&
  - configuration.expandtab
  + vimState.editor.options.insertSpaces
  ) {
  // We're in the leading whitespace - delete a tabstop
  const tabSize = vimState.editor.options.tabSize as number;
  