[Frontend] Internalize createDependencyTracker

Expand the FrontendOptions to allow the enabling
of the dependency tracker for non-system
dependencies, and switch the previous clients of
`createDependencyTracker` over to using this
option. This ensures that the dependency tracker
is now set only during `CompilerInstance::setup`.

lib/AST/ModuleLoader.cpp

@@ -30,14 +30,15 @@ class FileCollector;
 namespace swift {
 
 DependencyTracker::DependencyTracker(
-    bool TrackSystemDeps, std::shared_ptr<llvm::FileCollector> FileCollector)
+    IntermoduleDepTrackingMode Mode,
+    std::shared_ptr<llvm::FileCollector> FileCollector)
     // NB: The ClangImporter believes it's responsible for the construction of
     // this instance, and it static_cast<>s the instance pointer to its own
     // subclass based on that belief. If you change this to be some other
     // instance, you will need to change ClangImporter's code to handle the
     // difference.
-    : clangCollector(ClangImporter::createDependencyCollector(TrackSystemDeps,
-                                                              FileCollector)) {}
+    : clangCollector(
+          ClangImporter::createDependencyCollector(Mode, FileCollector)) {}
 
 void
 DependencyTracker::addDependency(StringRef File, bool IsSystem) {