fix(neon): Fix undefined behavior in channel callbacks when there is a panic

[kjvalencik]

Summary

• Catches panics and converts to uncaughtException
• Throws uncaughtException if throwing
• Passes opaque exceptions through as JsBox

Significant Changes

• Return Err(Throw) in Channel::send no longer disappears. Instead it will cause an uncaughtException
• Panicking in Channel::send is no longer undefined behavior. Instead it will cause an uncaughtException

What

uncaughtException in pseudo code look like:

const error = new Error("General neon message describing that there was an exception and/or panic");

// Exception was thrown while executing
if (exception) {
    error.cause = exception;
}

// Panic occurred while executing
if (panic) {
    // We were able to downcast the panic as a `String` or `&str`
    if (panicMsg) {
        error.panic = new Error(panicMsg);
    } else {
        error.panic = new Error("Unknown panic");
        error.panic.cause = JsBox(panic);
    }
}

interface UncaughtException extends Error {
    message: string;
    
    cause?: Error;

    panic?: Error & {
        cause?: JsBox
    };
}

[dherman]

This is super clean and well-thought-out. 👨‍🍳 💋

I made a couple minor suggestions for clarity, but I don't think it needs a re-review unless you want it.