Utils: Consolidate the isRelative/isAbsolute implementations

Even if we do it wrong in corner cases, we should do it consistently.

Change-Id: I68d5a6e55ede889cb44bedb46d0ea545dae7ba2c
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/mesonprojectmanager/mesonprojectparser.cpp

@@ -81,9 +81,7 @@ QStringList toAbsolutePath(const Utils::FilePath &refPath, QStringList &pathList
                    std::cend(pathList),
                    std::back_inserter(allAbs),
                    [refPath](const QString &path) {
-                       if (Utils::FileUtils::isAbsolutePath(path))
-                           return path;
-                       return refPath.pathAppended(path).toString();
+                        return refPath.resolvePath(path).toString();
                    });
     return allAbs;
 }