Reverts #38175, which is not correct, since in fact we do need to
pre-quote the command and arguments for the shell when using
`SpawnInTerminal` (although we should probably change the API so that
this isn't necessary). Then, applies the same fix as #38565 to fix the
root cause of being unable to spawn the login task on macOS, or in any
case where the command/args contain spaces.

Release Notes:

- Fixed being unable to login with Claude Code or Gemini using the
terminal.