feat: Add deref function

[PeterStaev]

Makes compatible with NS Core modules 8.4

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• Tests for the changes are included.

What is the current behavior?

If you use JSC runtime with NS Core 8.4 you get errors that deref is not a function.

What is the new behavior?

Adds a deref function to WeakRef which is the same as get per the ES specs.

Fixes/Implements/Closes #[Issue Number].