Add support for deprecated features

[Mic92]

Depends on #15148

Motivation is being able to remove url literals in #15151 while still having a way to evaluate old nix code.

[Mic92]

This code is largely based on what Lix already added. Having the same option is beneficial for inter-operability.

[Mic92]

An alternative to this could be just printing warnings otherwise?

[Mic92]

This one suggested warnings? #10281

[xokdvium]

Yeah I think the less deceptive approach would be #10262. The actual design of the options isn't final and needs some massaging, but the idea is good - just needs an implementation.

[dpulls]

🎉 All dependencies have been resolved !

[Ericson2314]

Suggested change

	Deprecated features that are enabled. (Currently there are none.)
	Deprecated features that are enabled.

Seems like that's not true with URL literals?

[Mic92]

yeah, but that's introduced in the next PR and not this one.

[Ericson2314]

I do think it would be better if URL literals was an eval setting rather than overall setting.

[Mic92]

I do think it would be better if URL literals was an eval setting rather than overall setting.

Shouldn't be a big deal to move, but I am not so sure if all "warnings" would be in the eval category: #10281 (comment)

[roberth]

deprecated-features = foo reads like enabling the deprecation of feature foo.
Option names should be unambiguous.
Another problem with this option is that there's no individual overriding like you would have with the warnings infrastructure that builds nicely on the options system.

[Ericson2314]

#15326 subsumes this