Various Plugins: Simplify return QStringList statements

Change-Id: Id014225851e6b9f8436387c681bea42e5de3b797
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/genericprojectmanager/genericproject.cpp

@@ -398,7 +398,7 @@ static QStringList readFlags(const QString &filePath)
 {
     const QStringList lines = readLines(filePath);
     if (lines.isEmpty())
-        return QStringList();
+        return {};
     QStringList flags;
     for (const auto &line : lines)
         flags.append(ProcessArgs::splitArgs(line, HostOsInfo::hostOs()));