Various Plugins: Simplify return FilePath statements

Change-Id: Ia9efb86f722caca1492b577d51442f1f23b804b4
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/cmakeprojectmanager/cmakebuildconfiguration.cpp

@@ -1567,7 +1567,7 @@ FilePath CMakeBuildConfiguration::shadowBuildDirectory(const FilePath &projectFi
                                                        BuildConfiguration::BuildType buildType)
 {
     if (projectFilePath.isEmpty())
-        return FilePath();
+        return {};
 
     const QString projectName = projectFilePath.parentDir().fileName();
     const FilePath projectDir = Project::projectDirectory(projectFilePath);