White Swan

• Preserve preexisting PROMPT_COMMAND as precmd function and DEBUG trap as a preexec function
• Preexec returns last error code from preexec functions
• Specify using builtin history in case users alias history. Fixes #55 and addresses https://gitlab.com/gnachman/iterm2/issues/6063
• Couple of test fixes.

Shout outs to @dimo414 and @jombooth for PRs in this cut 👍 🙏 🎉

• Thanks @gnachman for the continued usage and awesome work on iterm2