Improve JS compatibility by using types that are supported by JS

[hnorkowski]

🚀 Feature Request

Current Problem

Some of the types we expose are not supported by JavaScript. These types can only be passed to other functions that take them as arguments, but it is not possible to access or modify their data.

Proposed Solution

To improve the usability of our library in JavaScript it should be evaluated if some unsupported types can be replaced by supported types.

Additional Context

Such a change was already done by changing the type of placement in TextWatermarker from Sequence<..> to List<..> (see here)

Related: #40

[hnorkowski]

It seems like using toList() is not sufficient. If the list is empty an EmptyList type is return which is not supported by JS. For compatibility with not only JS but also Java we should consider changing all types involving lists to Array or ArrayList. These types seem to be fully supported by JS and Java.