Accept non-process arguments in functions for easier testing

Describe the enhancement
Maybe I missed something completely, but it'd be great for functions like core.getInput or core.setOutput to take a NodeJS.ProcessEnv object as an optional argument, defaulting to process.env, to make testing JS actions easier and cleaner.

Code Snippet
If your action code is something like

import * as core from "@actions/core";

const myInput = core.getInput("my_input_var"); 

it could be something like

import * as core from "@actions/core";

const myInput = core.getInput("my_input_var", undefined /* options */, {
  INPUT_MY_INPUT_VAR: "some-value",
});

Additional information
Again, if that's already possible, sorry for the extra toil!

Start with the @actions/core implementations for getInput and setOutput and their surrounding tests, then trace how process.env is accessed. Done means the relevant APIs accept an optional environment object while preserving existing defaults, with tests covering injected values.