better stringify key in LAZY_IN_SYNC

[paul-marechal]

Description

• When LAZY_IN_SYNC is invoked with a symbol it might throw an error because the JS runtime doesn't know how to stringify a symbol on its own for some reason.
• When passing a function/class as key, then the output gets weird as the JS runtime may return the whole class body when stringifying it.

This PR adjusts the way the key is stringified by:

• If it's a function then print as [function/class NAME].
• If it's a symbol then we explicitly convert it to string using symbol.toString() before printing.
• Wrap with single quotes in a template string.

Related Issue

#1510

Motivation and Context

Better error message.

How Has This Been Tested?

Manually called LAZY_IN_SYNC with a symbol using the node REPL.

Types of changes

• Updated docs / Refactor code / Added a tests case (non-breaking change)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have updated the changelog.