When scanning finds a dependency in the same package, do not load
public/private swiftinterface since they do not have the package level
decl to compile the current module. Always prefer package module (if
enabled), or use binary module, unless it is building a public/private
swiftinterface file in which case the interface file is preferred.
This also does some clean up to sync up the code path between implicit
and explicit module finding path.
rdar://122356964
Add a new flag to enable package interface loading.
Use the last value of package-name in case of dupes.
Rename PrintInterfaceContentMode as InterfaceMode.
Update diagnostics.
Test package interface loading with various scenarios.
Test duplicate package-name.
ambiguity during lookup when there are multiple public or inlinalbe
package decls in public interfaces. This PR adds a package name to
public swiftinterface and lets typecheck look up the package name
to narrow down the scope of access to package decls from an external
module.
Resolves rdar://117699160
