feature-request: improve compilation checks for missing symbols

Please add a check so that compilation fails (instead of runtime error) in case of the following code:

import Toybox.Application;
using Toybox.Application as App;
import Toybox.Application.Properties;
import Toybox.Lang;

function getConfigNumber(key as PropertyKeyType, defaultValue as Number) as Number {
    var value = getConfig(key);
    if (value != null && !(value instanceof Lang.Number)) {
        if (value instanceof String) { // in this line
            value = value.toNumber();
        } else if (value instanceof Boolean) { // and this line
            value = value ? 1 : 0;
        }
    }
    if (value == null) {
        value = defaultValue;
    }
    return value;
}

In the above code at least on some devices (i.e: vívoactive® 4: 6.90 ) I got an error: Error Name: Symbol Not Found Error
On the line: value instanceof String

This could be easily caught during compilation.