[Serialization] Load indirect package dependencies from the current package

When loading a swiftmodule A, read its package information to tell if
the current client should load A's dependencies imports by a package
import. Only clients belonging to the same package as A should load
those dependencies, clients outside of the package likely don't have
access to those dependencies.

This is specific to swiftmodules as swiftinterfaces never display a
package-only import. Clients are unaware of package dependencies when
building against a swiftinterface.

rdar://106164813

lib/Serialization/SerializedModuleLoader.cpp

@@ -426,6 +426,10 @@ llvm::ErrorOr<ModuleDependencyInfo> SerializedModuleLoaderBase::scanModuleFile(
     if (dependency.isImplementationOnly())
       continue;
 
+    if (dependency.isPackageOnly() &&
+        Ctx.LangOpts.PackageName != loadedModuleFile->getModulePackageName())
+      continue;
+
     // Find the top-level module name.
     auto modulePathStr = dependency.getPrettyPrintedPath();
     StringRef moduleName = modulePathStr;