test: Add tests for private methods and accessors productions

src/class-elements/rs-private-getter-alt.case

src/class-elements/rs-private-getter.case

src/class-elements/rs-private-method-alt.case

src/class-elements/rs-private-method.case

src/class-elements/rs-private-setter-alt.case

src/class-elements/rs-private-setter.case