ghost_head cleanup & debug statements

[ErisDS]

This adds 3 cleanup / minor change commits on top of the error handling PR #8982.

• Adds a handful of debug statements, so it's easier to see where time is spent after rendering when in DEBUG mode.
• Changes the layout of promises to always have the . on a newline, which makes it easier to read
• Changes from using Promise.props to Promise.join, which allows us to remove a few lines of code that otherwise don't do much

It would be possible to squash and merge this instead of #8982, setting the commit message back to the error handling one.

[kirrg001]

I would squash these together and stick with the general commit message ghost_head cleanup & debug statements. The single commit messages are a bit too general e.g. Use join instead of props for less code - doesn't say where. If you want single commits, could you pls update the single messages? 🙃

[ErisDS]

It would be possible to squash and merge this instead of #8982, setting the commit message back to the error handling one.

This comment was if you merged this instead of #8982 as all 4 commits were here ;) Definitely squash this and give it a general message without an emoji!