[clang-tools-extra] Add --project-root to clangd (PR #155905)

[Nathan Ridge via cfe-commits]

================
@@ -35,6 +35,8 @@ struct ProjectInfo {
 /// Provides compilation arguments used for parsing C and C++ files.
 class GlobalCompilationDatabase {
 public:
+  GlobalCompilationDatabase(std::optional<std::string> WorkingDirectory)
----------------
HighCommander4 wrote:

I would give this parameter a default to minimize the disruption caused by this change. (I'm not just talking about test code in this repo; I think this class has out-of-tree subclasses as well.)

https://github.com/llvm/llvm-project/pull/155905