[clang] [clang-tools-extra] [clang][deps] Make the service provide the VFS (PR #181424)

[Qiongsi Wu via cfe-commits]

================
@@ -109,9 +109,7 @@ ModuleDependencyScanner::scan(PathRef FilePath,
 
   using namespace clang::tooling;
 
-  llvm::SmallString<128> FilePathDir(FilePath);
-  llvm::sys::path::remove_filename(FilePathDir);
-  DependencyScanningTool ScanningTool(Service, TFS.view(FilePathDir));
----------------
qiongsiwu wrote:

Could you help me understand why the removed code `TFS.view(FilePathDir)` is equivalent to the new code where we call `TFS.view(std::nullopt);`? 

https://github.com/llvm/llvm-project/pull/181424