Add protocol command to disable the listing of playlists in the root folder for the lsinfo command.

[jcorporation]

From #2102:

I can imagine 4 ways dealing with this deprecation:
1. leave it as it is, forever
2. remove it completely
3. make it a per-connection setting
4. make it a global config option

This is 4, but I fear it's the worst way. No user knows about this protocol-level detail and no user should have to know about this. This means no client can ever take advantage of this. 1 is bad because nobody likes to support deprecated legacy stuff, and it may require client-side kludges to suppress it. 2 is bad because some random client may rely on this, and if somebody complains, they're right.

3 seems like the best way to deal with this: every client can decide; newer clients can explicitly opt into new protocol semantics, easily. We just need a protocol command for such an opt-in. I had been thinking about this a few times, but never came up with a design.

We have something similar with tag types: the "old" way to enable/disable tag types is the metadata_to_use setting, but this discards tags while scanning; it's a fragile design that doesn't allow clients to opt-in and opt-out, meaning either they have too much protocol overhead or not enough information. Then I added a tagtypes command which allowed clients to choose exactly which tag types they were interested in. This is fully backwards compatible, but allows modern clients to reduce overhead.

[jcorporation]

2 is bad because some random client may rely on this, and if somebody complains, they're right.

You mark this behavior as obsolete since years, but you will never deactivate it? I would prefer to remove it, but it is your decision.

I think we should introduce a general command so that we can make further behavioral changes opt-in. and add also a command to list the deprecated behavioral's or add it as output to the config command.

[jcorporation]

#2123