[WIP] Callback for repl module evaluator using default_js_slang

[8kdesign]

Description

Do not merge. Just a hacky sample code for how result of default_js_slang can be obtained.
If possible, default_js_slang should be modified to process and return the result.

Added ability to receive callback with result when default_js_slang is used in repl module.

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules