CMakePM: Add support for qtc_runnable feature

This will allow for the Qt Creator's CMake build only qtcreator
target to be selected as runnable.

Similar to qmake's qtc_runnable or Qbs's qtcRunnable features.

Fixes: QTCREATORBUG-25908
Change-Id: I6416873d0ad9cfec4960d98fc4b289ec98cc58b1
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cmakeprojectmanager/fileapidataextractor.cpp

@@ -256,6 +256,8 @@ QList<CMakeBuildTarget> generateBuildTargets(const PreprocessedData &input,
                                                                  || f.fragment.contains("Qt6Gui"));
                                                   });
 
+                ct.qtcRunnable = t.folderTargetProperty == "qtc_runnable";
+
                 // Extract library directories for executables:
                 for (const FragmentInfo &f : t.link.value().fragments) {
                     if (f.role == "flags") // ignore all flags fragments