Add a way to change script working directory

[CompeyDev]

An API for changing the directory of a script (namely process.chdir), would be useful to for traversing directories at runtime, instead of being locked into the directory lune run was invoked from.

Potential Design

function process.chdir(dir: string): () end

Drawbacks

This would potentially involve a breaking change, since process.cwd can no longer be a static string computed at builtin initialization time. Instead, it would need to do be a function which dynamically returns the current directory.