Clang: Make file ids unique

Clang file ids are only unique for one query. Because we query in parallel
we have to manage our own unique ids.

Change-Id: I67d57d8b1766cab75ad252a14e57bbf9dc5fdb79
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/tools/clangrefactoringbackend/source/clangtool.h

@@ -77,13 +77,13 @@ struct FileContent
 
 struct UnsavedFileContent
 {
-    UnsavedFileContent(Utils::SmallString &&filePath,
+    UnsavedFileContent(Utils::PathString &&filePath,
                        Utils::SmallString &&content)
         : filePath(std::move(filePath)),
           content(std::move(content))
     {}
 
-    Utils::SmallString filePath;
+    Utils::PathString filePath;
     Utils::SmallString content;
 };