Add isEmptyRecord function

[aleclarson]

Using TypeScript's definition of "Record" (see the Record<K, V> generic type).

This checks if a plain object has 0 “own keys” inside. Inherited keys (e.g. prototype) are not checked. It does this in the most efficient way possible (for…in with early return).

Steps:

• for…in loop
• use Object.prototype.hasOwnProperty.call
• return false if hasOwnProperty check passes
• return true after the loop