Set working directory to current source

[gadenbuie]

It'd be super helpful to be able to set the current working directory to the directory of the open and active source file. (There's a similar action in RStudio.) This is useful when you're working on a large project with "subprojects", e.g. several Shiny apps, and it's useful to jump into the context where the script will run.

I think this is a feature request, but maybe it's possible to set up this action with existing commands.

I guess to be feature complete, it'd also be useful to have a command to return to the project directory.