CMakePM: Do not show source/group/path twice

For the cases of:
  source_group(TREE ${CMAKE_SOURCE_DIR} FILES my/subdir/file.cpp)

Treat the "my\\subdir" part in the project view as part of the source
group name.

Fixes: QTCREATORBUG-29799
Change-Id: I92bf581be25d085783bcdadd8a418b849a29c708
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/cmakeprojectmanager/fileapidataextractor.cpp

@@ -664,7 +664,10 @@ static void addCompileGroups(ProjectNode *targetRoot,
                                                              sourceDirectory,
                                                              targetRoot);
         if (showSourceFolders) {
-            insertNode->addNestedNodes(std::move(current), sourceDirectory);
+            FilePath baseDir = sourceDirectory.pathAppended(td.sourceGroups[i]);
+            if (!baseDir.exists())
+                baseDir = sourceDirectory;
+            insertNode->addNestedNodes(std::move(current), baseDir);
         } else {
             for (auto &fileNodes : current)
                 insertNode->addNode(std::move(fileNodes));