Feature request: Warn when adding song that already exists in music playlist

Description

When adding a song to a music playlist, it would be very helpful to receive a warning if that song is already present in the playlist, with the ability to abort the operation and not add a duplicate song to the playlist.

Expected behavior

A use case for this feature is as follows: I own many albums and have curated a playlist of the songs I want in rotation while driving. This playlist has around 1000 songs. When I am playing a whole album and I hear a song that I want to be present in that playlist, I try to add it to the playlist. If it is not in the playlist, it is added. If it is already in the playlist, I see a warning and can choose not to add a duplicate.

The current behavior in VLC 3.2.12 is that the song is added to the playlist regardless of whether or not it is already present in that playlist. Without this feature, I have to go into the playlist of 1000 songs and check if that song is already present, and if it is not, go back to the album to add the song to the playlist.

Screenshot / video

For example, the Google Play Music app issues this warning when the user attempts to add a song which is already present in the playlist:

App mode

Smartphone

TV

Auto