Support UTF-8 encoded emojis in NINJA_STATUS environment variable

[jthackray]

Similar to #713, it would be great if NINJA_STATUS accounted for the width of UTF-8 encoded emojis. I've written a fix for this in #2727 which works for me, so I can use:

  export NINJA_STATUS=$(print -P "%B%F{magenta}🧵%%r 🚀%%o/s %F{green}⏱️%%w ⌛%%W %F{cyan}%%f/%%t %F{yellow}%%p%b %F{reset}")

and the full terminal width is used. Ideally, in the patch, I would have used wcwidth() but I believe this isn't available on Windows, so the code assumes UTF-8 emojis are 2 characters in width (apart from control characters), which is true on iTerm2 and probably most other terminal emulators.

I've added new tests for this, and the existing tests continue to pass.

Comments appreciated. Thanks :)