Revisit error message specificity and clarity

[jye-sf]

Some of our error messages could definitely be improved to be more specific about what is happening and how the issue might be resolved.

Specific pain point errors should be addressed. Additional time could be time-boxed to evaluate other error messages and how they can be improved.

Errors to be addressed:

• INVALID_IDENTIFIER - could be more specific when issue is due to ES6 reserved words.

[git2gus]

This issue has been linked to a new work item: W-18040860