Clean empty arrays and objects

[dmitryashutov]

According to FHIR spec a resource can not contain undefined, null or empty array values:

• remove key/value pair if the value is empty array
• remove key/value pair if the value is undefined

[ruscoder]

Let's add filterValues() function similar to mapValues for better readability

[ruscoder]

function filterValues(obj: object, fn: (value: any, key: string) => any) {
    return Object.fromEntries(
        Object.entries(obj).filter(([key, value]) => {
            return [key, fn(value, key)];
        }),
    );
}

[ruscoder]

}```