Deprecate `Readable.readableFlowing` setter

[ronag]

How this works and what it does is pretty undefined and I don't think users should be using this setter.

[ronag]

@nodejs/streams

[mcollina]

I'm +1. I think I added it because we needed it somewhere in core.

[ronag]

There might be one case where it makes sense to have it: https://github.com/nodejs/undici/blob/main/lib/client.js#L723-L733

Not sure how we could work around that. Maybe change undici so it uses read() + 'readable'.

[Mesteery]

It is also used in :

node/lib/_http_client.js

Line 523 in 533cafc

socket.readableFlowing = null;

node/lib/_http_server.js

Line 719 in 533cafc

socket.readableFlowing = null;

node/lib/net.js

Line 384 in 533cafc

this.readableFlowing = false;

node/lib/internal/child_process.js

Line 438 in 533cafc

stream._stdio.readableFlowing = false;

[ronag]

It's probably easier to keep using it there than fixing it. I'm more concerned with the public api to our users.