How to get PropertyDeclaration's from extends.

[Hugos68]

Let's say I have:

interface InterfaceOne {
	propertyOne: string
}

interface InterfaceTwo extends InterfaceOne {
	propertyTwo: string
}

const interface = sourceFile.getInterface("interfaceTwo")

console.log(interface.getProperties().length) // 1

How can I get all properties, including those that are extended from?
Use case: We're building automated documentation and need to extract all properties (including extended one's) to document them.