It is unsound to expose `package` declarations in textual interfaces without a
package identity for them to belong to so we should not offer this flag.
Resolves rdar://139361524.
ValueDecl::isInterfacePackageEffectivelyPublic is used to check if a package decl in
interface file can be skipped for typecheck; if the decl is inlinable and in public or
private interface, it should be allowed to skip. This PR adds a missing check which
looks up the Interface source kind.
Resolves rdar://135388095
Having package-name printed in public or private interface led to strange dependency errors in the past. For example, an SPI module is a dependency within a package, but due to the package-name being printed in public or private interface, dependency scanner tries to find it even for an external client of the package, causing a `no such module found` error. The -disable-print-package-name-for-non-package flag helps with such case, but to enforce the correct behavior, we should make it a default to not print package-name in public or private interface.
Resolves rdar://135260270
Having package-name flag in non-package interfaces causes them to be built as if
belonging to a package, which causes an issue for a loading client outside of the
package as follows.
For example, when building X that depends on A with the following dependency chain:
X --> A --> B --(package-only)--> C
1. X itself is not in the same package as A, B, and C.
2. When dependency scanning X, and opening up B, because the scan target is in a
different package domain, the scanner decides that B's package-only dependency
on C is to be ignored.
3. When then finally building A itself, it will load its dependencies, but because
the .private.swiftinterface of A still specifies -package-name, when it loads
B, it will then examine its dependencies and deem that this package-only dependency
on C is required.
Because (2) and (3) disagree, we get an error now when building the private A textual interface.
rdar://130701866
