Implement Value Extraction from Scopes

[iamrecursion]

Summary

In order to implement lazy visualisations, a key feature of Enso Studio, we need the ability to execute arbitrary Enso code on values in the current frame. This execution mustn't be able to change the values in the scope, so we need to have some method for extracting those values from those scopes.

Value

This is the first of the two major building blocks to being able to provide lazy visualisations for Enso Studio.

Specification

• Determine how best to extract values from the introspected scope in the interpreter without allowing any alteration to these values.
• This value extraction should not impose significant performance or memory penalties, even in the case where the values contain huge amounts of data.
• Implement this extraction functionality into the existing interpreter and provide an API.

Acceptance Criteria & Test Cases

• The interpreter provides an API that allows for extracting values from the introspected interpreter scope.
• This functionality is robust and rigorously tested.

[iamrecursion]

Landed in #419.