Naming "struct" interface getter methods

[infeo]

As mentioned in PR https://github.com/cryptomator/jfuse/pull/19#discussion_r999135527, currently the naming convention for getters in struct interfaces is mixedbetween

• record-style: if field is called foo, the getter is also called foo() and
• java-style: if field is called foo, the getter is called getFoo()

Before reaching 1.0.0 we should decide what naming convention to use to offer a unified API.