[CAS][DependencyScanning] Don't keep a shared state of common file deps

Unlike `swift-frontend -scan-dependencies` option, when dependency
scanner is used as a library by swift driver, the SwiftScanningService
is shared for multiple driver invocations. It can't keep states (like
common file dependencies) that can change from one invocation to
another.

Instead, the clang/SDK file dependencies are computed from each driver
invocations to avoid out-of-date information when scanning service is
reused.

The test case for a shared Service will be added to swift-driver repo
since there is no tool to test it within swift compiler.

lib/Serialization/ModuleDependencyScanner.cpp

@@ -174,6 +174,14 @@ ErrorOr<ModuleDependencyInfo> ModuleDependencyScanner::scanInterfaceFile(
     std::string RootID;
     if (dependencyTracker) {
       dependencyTracker->startTracking();
+      dependencyTracker->addCommonSearchPathDeps(Ctx.SearchPathOpts);
+      std::vector<std::string> clangDependencyFiles;
+      auto clangImporter =
+          static_cast<ClangImporter *>(Ctx.getClangModuleLoader());
+      clangImporter->addClangInvovcationDependencies(clangDependencyFiles);
+      llvm::for_each(clangDependencyFiles, [&](std::string &file) {
+        dependencyTracker->trackFile(file);
+      });
       dependencyTracker->trackFile(moduleInterfacePath);
       auto RootOrError = dependencyTracker->createTreeFromDependencies();
       if (!RootOrError)