Jukebox song registries are experimental and don't update on /reload

When enabling/disabling datapacks that contain jukebox_song entries, the world needs to be restarted for the song registry to update.

Steps to reproduce:

1. Create a datapack (lets call it 'example') with a custom jukebox_song (lets call that 'custom_song')
   example
       - pack.mcmeta
       - data
           - example
               - jukebox_song
                   - custom_song.json
2. /datapack enable "file/example"
3. Run

   /give @s dirt[minecraft:jukebox_playable={"song":"example:custom_song"}]

Observed result:
Malformed 'minecraft:jukebox_playable' component: 'Failed to parse either. First: failed to get element example:custom_song; Second: Cannot parse as key without registry'

Expected result:
The jukebox_song from the newly added datapack is recognized as a valid value for the jukebox_playable component.

However when restarting the world after enabling the datapack, the jukebox_song registry is filled correctly and contains the new song(s).

1. /datapack enable "file/example"
2. Restart the server or exit and re-enter the world
3. Run

   /give @s dirt[minecraft:jukebox_playable={"song":"example:custom_song"}]

This produces the expected behaviour and creates a dirt block with a jukebox_playable component.