[Sema] Don't check availability in assigned properties initializers for -check-api-availaiblity-only mode

[xymus]

For a non-public property where the type is defined by an assignment, like internal var internalAssigned = NewStruct(), type-checking the type's availability is done via checking the initializer expression.

In -check-api-availaiblity-only mode, pass down a flag to not check availability in expressions for initializer expressions of such non-public properties.

To make sure this doesn't have unintended side-effects on generated code, forbid IR generation when the flag -check-api-availaiblity-only is used.

rdar://84389825

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Followup to #39640.

[xymus]

@swift-ci Please smoke test

[xymus]

cc @davidungar for your interest in availability issues.

This is part of the work started in #39640 that introduced a mode to check the availability of the public API only. This is to be used when we are not generating a binary but only the module files including swiftinterfaces.

[davidungar]

Thanks for thinking of me. I haven't looked at it yet but right off the bat, it would help if the summary clarified the purpose of the PR. Is it to speed up compilation in a certain scenario? Or is it to improve type checking in some other way?

[davidungar]

LGTM

[xymus]

@davidungar The -check-api-availablity-only flag toggles an availability checking mode appropriate for projects building only a module interface and no binaries. This applies to Swift only frameworks that are backported to armv7 on iOS, these archs never had support for Swift frameworks in the OS but we still want the compiler to see the (unavailable) module content when targetting these archs. For such a case, -check-api-availablity-only ends up checking only what will be in the module interface (API, SPI, inlinable code, etc.) and skip functions bodies and other internal details.

[xymus]

Currently some of these projects disable availability checking all together, which is very very bad. This mode should be more appropriate to their needs, raising only errors relevant to their use cases.

[nkcsgexi]

Makes sense to me!

[xymus]

This is a different implementation. Skipping the whole type checking lead to errors at serialization as skipping function bodies doesn't skip property initialization.

Instead, let's pass down a flag to disable availability checking in expression when type-checking the property initializer.

@swift-ci Please smoke test

[xymus]

@swift-ci Please smoke test Linux