serialization: obfuscate the serialized search paths

We noticed some Swift clients rely on the serialized search paths in the module to
find dependencies and droping these paths altogether can lead to build failures like
rdar://85840921.

This change teaches the serialization to obfuscate the search paths and the deserialization
to recover them. This allows clients to keep accessing these paths without exposing
them when shipping the module to other users.

lib/Serialization/ModuleFileSharedCore.h

@@ -149,7 +149,7 @@ private:
   SmallVector<Dependency, 8> Dependencies;
 
   struct SearchPath {
-    StringRef Path;
+    std::string Path;
     bool IsFramework;
     bool IsSystem;
   };
@@ -374,7 +374,7 @@ private:
       std::unique_ptr<llvm::MemoryBuffer> moduleDocInputBuffer,
       std::unique_ptr<llvm::MemoryBuffer> moduleSourceInfoInputBuffer,
       bool isFramework, bool requiresOSSAModules,
-      serialization::ValidationInfo &info);
+      serialization::ValidationInfo &info, PathObfuscator &pathRecoverer);
 
   /// Change the status of the current module.
   Status error(Status issue) {
@@ -464,7 +464,7 @@ private:
   /// Loads data from #ModuleDocInputBuffer.
   ///
   /// Returns false if there was an error.
-  bool readModuleDocIfPresent();
+  bool readModuleDocIfPresent(PathObfuscator &pathRecoverer);
 
   /// Reads the source loc block, which contains USR to decl location mapping.
   ///
@@ -474,7 +474,7 @@ private:
   /// Loads data from #ModuleSourceInfoInputBuffer.
   ///
   /// Returns false if there was an error.
-  bool readModuleSourceInfoIfPresent();
+  bool readModuleSourceInfoIfPresent(PathObfuscator &pathRecoverer);
 
   /// Read an on-disk decl hash table stored in
   /// \c sourceinfo_block::DeclUSRSLayout format.
@@ -510,12 +510,13 @@ public:
        std::unique_ptr<llvm::MemoryBuffer> moduleDocInputBuffer,
        std::unique_ptr<llvm::MemoryBuffer> moduleSourceInfoInputBuffer,
        bool isFramework, bool requiresOSSAModules,
+       PathObfuscator &pathRecoverer,
        std::shared_ptr<const ModuleFileSharedCore> &theModule) {
     serialization::ValidationInfo info;
     auto *core = new ModuleFileSharedCore(
         std::move(moduleInputBuffer), std::move(moduleDocInputBuffer),
         std::move(moduleSourceInfoInputBuffer), isFramework,
-        requiresOSSAModules, info);
+        requiresOSSAModules, info, pathRecoverer);
     if (!moduleInterfacePath.empty()) {
       ArrayRef<char> path;
       core->allocateBuffer(path, moduleInterfacePath);