R.string.next should be splitted in two

Description

It has different translations between the playback next feature and the "next step" used in the onboardings.

changed milestone to %3.5.x

added UI label

assigned to @Aza

mentioned in issue #2446 (closed)

english: play next/next file/skip forward, next/next step
chinese: 下一个(next one)/下一集(next ep)/前进(forward)/etc., 前进(forward)/下一步(next step)
chinese for https://code.videolan.org/videolan/vlc-android/-/blob/master/application/resources/src/main/res/values/strings.xml#L653 could use just 下一个 or just 前进 for both play next and next step too

wonder what about other languages?

closed with commit c200c9d3