[DependencyScan] Propagate module library level through dependency scanner for CAS builds

Compute and propagate the library level (api/spi/ipi) of each module
dependency through the dependency scanner so that the compiler can
correctly enforce private module import diagnostics in CAS mode, where
path-based SPI detection fails because CAS abstracts file paths to
content IDs.

Swift modules:
- Detect library level from the module interface path using
  libraryLevelFromPath() during scanning, for both textual (.swiftinterface)
  and binary (.swiftmodule) Swift modules.

Clang modules:
- Expose ModuleMapIsPrivate from clang::Module in ModuleDeps via the
  dependency scanning infrastructure.
- Set library level for clang modules in bridgeClangModuleDependency()
  using ModuleMapIsPrivate (catches module.private.modulemap in any
  SDK location) and libraryLevelFromPath() on the module map file
  (catches modules under PrivateFrameworks directories).

The library level is:
- Stored in ModuleDependencyInfo and serialized in the module dependency
  cache (format version bumped to v8).
- Exposed through the swiftscan C API via a new
  swiftscan_module_info_get_library_level() function (API minor version
  bumped to 3).
- Emitted in the dependency scanner JSON output as "libraryLevel" for
  all module kinds (Swift textual, Swift binary, Clang, and main module).
- Parsed from the explicit module map JSON by ExplicitModuleMapParser
  for both Swift (ExplicitSwiftModuleInputInfo) and Clang
  (ExplicitClangModuleInputInfo) modules.
- Looked up in ModuleLibraryLevelRequest via
  ASTContext::getExplicitModuleLibraryLevel(name, isClang), which
  consults the appropriate map (Swift or Clang) based on module kind.

rdar://172693314

Assisted-By: Claude

lib/DependencyScan/ModuleDependencyCacheSerialization.cpp

@@ -232,10 +232,11 @@ bool ModuleDependenciesCacheDeserializer::readGraph(
 
   std::vector<ScannerImportStatementInfo> importStatements;
   std::vector<ScannerImportStatementInfo> optionalImportStatements;
+  LibraryLevel currentLibraryLevel = LibraryLevel::Other;
 
   auto addCommonDependencyInfo =
-      [&importedClangDependenciesIDs, &macroDependencies]
-      (ModuleDependencyInfo &moduleDep) {
+      [&importedClangDependenciesIDs, &macroDependencies,
+       &currentLibraryLevel](ModuleDependencyInfo &moduleDep) {
         // Add qualified dependencies of this module
         moduleDep.setImportedClangDependencies(importedClangDependenciesIDs);
 
@@ -244,6 +245,7 @@ bool ModuleDependenciesCacheDeserializer::readGraph(
           moduleDep.addMacroDependency(md.first, md.second.LibraryPath,
                                        md.second.ExecutablePath);
 
+        moduleDep.setLibraryLevel(currentLibraryLevel);
         moduleDep.setIsFinalized(true);
       };
 
@@ -477,7 +479,8 @@ bool ModuleDependenciesCacheDeserializer::readGraph(
           importedSwiftDependenciesIDsArrayID,
           importedClangDependenciesIDsArrayID,
           crossImportOverlayDependenciesIDsArrayID,
-          swiftOverlayDependenciesIDsArrayID, moduleCacheKeyID;
+          swiftOverlayDependenciesIDsArrayID, moduleCacheKeyID,
+          libraryLevelValue;
 
       ModuleInfoLayout::readRecord(Scratch, moduleNameID, moduleImportsArrayID,
                                    optionalImportsArrayID, linkLibraryArrayID,
@@ -486,7 +489,7 @@ bool ModuleDependenciesCacheDeserializer::readGraph(
                                    importedClangDependenciesIDsArrayID,
                                    crossImportOverlayDependenciesIDsArrayID,
                                    swiftOverlayDependenciesIDsArrayID,
-                                   moduleCacheKeyID);
+                                   moduleCacheKeyID, libraryLevelValue);
       auto moduleName = getIdentifier(moduleNameID);
       if (!moduleName)
         llvm::report_fatal_error("Bad module name");
@@ -544,6 +547,7 @@ bool ModuleDependenciesCacheDeserializer::readGraph(
       if (!optionalMacroDependencies)
         llvm::report_fatal_error("Bad Macro Dependencies info");
       macroDependencies = *optionalMacroDependencies;
+      currentLibraryLevel = static_cast<LibraryLevel>(libraryLevelValue);
       break;
     }
 
@@ -1598,7 +1602,8 @@ void ModuleDependenciesCacheSerializer::writeModuleInfo(
           ModuleIdentifierArrayKind::CrossImportOverlayDependenciesIDs),
       getIdentifierArrayID(
           moduleID, ModuleIdentifierArrayKind::SwiftOverlayDependenciesIDs),
-      getIdentifier(dependencyInfo.getModuleCacheKey()));
+      getIdentifier(dependencyInfo.getModuleCacheKey()),
+      static_cast<unsigned>(dependencyInfo.getLibraryLevel()));
 
   switch (dependencyInfo.getKind()) {
   case swift::ModuleDependencyKind::SwiftInterface: {