fix: keep NODE_OPTIONS unset when the calculated value is empty

[DanielRose]

Also update the type of the process-environment to NodeJS's, which allows undefined as valid value.

What's the problem this PR addresses?

Resolves #6148

How did you fix it?

If the calculated NODE_OPTIONS value is an empty string, set the environment value to undefined.

Since the original definition of the process-environment did not allow undefined, I changed the type definition to use NodeJS.ProcessEnv. Otherwise the code would need to be written as

env.NODE_OPTIONS = nodeOptions ? nodeOptions : undefined as unknown as string;

I haven't figured out where this could be tested, so I did not add/update any unit tests.

Checklist

• I have read the Contributing Guide.
• I have set the packages that need to be released for my changes to be effective.
• I will check that all automated PR checks pass before the PR gets reviewed.