Built-in support for OSC9;4

[zkat]

Various terminals now support OSC9;4, which lets you update terminal status bars themselves with progress details. It would be wonderful if something like this were built-in to indicatif, and probably isn't a lot of work to integrate. See microsoft/terminal#6700

[djc]

I'm open to having support for this, but unlikely to be motivated to implement it myself.

[chris-laplante]

Yes, please feel free to submit a PR!