Expression 2: Add `@feature` directive for enabling backwards-uncompatible features, replace `@strict` with `@feature edition1`

[stepa2]

Wiremod updates have broken my chips fairly often, and it affected other players whom I gave my chips to.
I propose to disable new backwards-uncompatible changes unless they is enabled by @feature directive
and to stop adding new backwards-uncompatible changes enabled by @strict.

@feature syntax and functionality

"Features" are used to enable backwards-uncompatibe features.

Feature F may require other features A and B to function, in this case enabling F enables A and B.

# Enable features
@feature featureOne featureTwo

You can explicitly disable feature A. If other features F and G require it, they are disabled too.

@feature F G randomFeature
# Disables A, F and G. randomFeature does not require any disabled feature so it keep working.
@feature -A

Except features with "latest" in name, no feature should ever be changed in way that break existing code, except on language edition deprecation.

@feature latest requires all the features available now.
@feature disable_deprecated_latest disallow usage of everything deprecated

Language edition features

I suppose it would be impractical to list all the features your chip uses.
To simplify, I suggest to add "edition"/"milestone"/?? features.
They add nothing by their own, but they enable other features.

I suggest deprecation of @strict in favour of @feature edition1.
Future features plus edition1 will form @feature edition2, and so on.

Maybe some features will never be added to an edition.

Language edition deprecation

If technical debt is too big, older @editions and features they require may be removed completely.
It is supposed to be rare event.

Example features

• @feature disable_returnless_functions that disallows function number example() { print("no return") }
• @feature disable_function_redifinition that causes #2910
• @feature disable_deprecated_before_edition1 that disallows usage of anything deprecated before edition1
• @feature swap_logical_short_circuit_ops that makes || a short-circuiting operation and | a non-short-circuiting one.

[Denneisk]

Vurv will probably say to move this to discussions but I think his intent was to add a @version directive.

[AlexALX]

@version might be good solution so we can make old chips still work or something. but not sure what happens if you will remove later older version support...