[Serialization] Move some package-only import logic from writer to reader

Let's centralize the logic deciding if we load a transitive dependency
on the client side and have the producer write the truth in the
swiftmodule.

Author: xymus

Diff for: lib/AST/Module.cpp

@@ -2124,7 +2124,7 @@ SourceFile::getImportedModules(SmallVectorImpl<ImportedModule> &modules,
     else if (desc.options.contains(ImportFlags::ImplementationOnly) ||
              (desc.accessLevel <= AccessLevel::Internal && moduleIsResilient))
       requiredFilter |= ModuleDecl::ImportFilterKind::ImplementationOnly;
-    else if (desc.accessLevel <= AccessLevel::Package && moduleIsResilient)
+    else if (desc.accessLevel <= AccessLevel::Package)
       requiredFilter |= ModuleDecl::ImportFilterKind::PackageOnly;
     else if (desc.options.contains(ImportFlags::SPIOnly))
       requiredFilter |= ModuleDecl::ImportFilterKind::SPIOnly;

Diff for: lib/Serialization/ModuleFileSharedCore.cpp

@@ -1694,6 +1694,8 @@ ModuleFileSharedCore::getTransitiveLoadingBehavior(
     return ModuleLoadingBehavior::Required;
   }
 
+  bool moduleIsResilient = getResilienceStrategy() ==
+                             ResilienceStrategy::Resilient;
   if (dependency.isImplementationOnly()) {
     // Implementation-only dependencies are not usually loaded from
     // transitive imports.
@@ -1712,7 +1714,8 @@ ModuleFileSharedCore::getTransitiveLoadingBehavior(
   if (dependency.isPackageOnly()) {
     // Package dependencies are usually loaded only for import from the same
     // package.
-    if (!packageName.empty() && packageName == getModulePackageName()) {
+    if ((!packageName.empty() && packageName == getModulePackageName()) ||
+        !moduleIsResilient) {
       return ModuleLoadingBehavior::Required;
     } else if (debuggerMode) {
       return ModuleLoadingBehavior::Optional;